• 1camshaft
• 2valves
• 3piston
• 4connecting rod
• 5crankshaft
• 6oil pan

Engine noises and knocking

108 guides in this section

The engine is the most talkative part of a car and the most ambiguous one: the word “knock” covers both the harmless clatter of injectors and worn crankshaft bearings, where every kilometre brings a rebuild closer. What separates them is not loudness but where the sound comes from, when it appears and how it reacts to the throttle and to warming up.

This section collects a guide for each type of sound: from valve ticking and timing-chain rustle to pinging and the knock of rod bearings. Each one comes with what it sounds like, safe checks you can do without taking anything apart, and an honest verdict on how urgent it is.

If you are not sure which sound is yours, start with the interactive question tree on the symptom pages below: a few questions narrow the field faster than reading every article in a row.

Where the noise comes from

engine bay

Narrow the sound down by questions

An interactive diagnosis tree: a few questions and the list of causes gets much shorter.

• Knocking in the engine
• Engine knock when cold
• Ticking engine
• Pinging when accelerating
• Vibration at idle
• Squeal on startup
• Belt squeal

All articles in this section

• 1.4 TSI timing chain rattle: the fault and the fix Why early chain-driven 1.4 TSI engines rattle on a cold start, how to tell a stretched chain from other knocks, and what the repair involves.
• A broken timing chain: consequences by engine What happens to an engine when the timing chain breaks or jumps, why some engines only need a new chain and others a cylinder head rebuild.
• A knock at start-up after standing for weeks Why an engine knocks for the first seconds after weeks parked: oil draining down, lifters, the chain tensioner, cam phasers. Where normal ends.
• A knock on lift-off A single knock as you release the throttle: worn engine mounts, driveline play, the timing chain, the exhaust. How to localise the source.
• A knock only with passengers or a load Empty, the car is quiet; with people and luggage a knock appears. What changes under load and which parts give themselves away exactly this way.
• A knock when releasing the clutch A knock as the clutch pedal comes up comes from the disc damper, the flywheel, the engine mounts and the driveshaft joints. How to tell them apart.
• A mechanic's stethoscope you can make yourself How to build a car stethoscope from a screwdriver, a hose or a tube, where to listen on the engine and accessories, and the safety rules to follow.
• A noise that only appears under load on a climb Why a stray noise is only heard on a climb under power, which parts behave that way, and how to tell the belt from a CV joint and detonation.
• A ringing under the car at idle A heat shield, a broken catalytic converter, the exhaust touching the body: where a ringing under the car at idle comes from and how to check it.
• A single clunk when pulling away and braking Where a single clunk when moving off and stopping comes from: pads, calipers, engine mounts, propshaft. How to check it and how the repair is decided.
• A squeal: the belt or an idler bearing A squeal under the bonnet comes from both a slipping belt and a dying idler bearing. How to tell them apart by the conditions in which the sound appears.
• A whining water pump: how to check it Why a water pump whines, how to tell its noise from the alternator and idler pulleys, simple checks without dismantling anything, and how the repair is decided.
• A/C compressor clutch: the sounds of failure Chattering, whining or grinding that appears exactly when the air conditioning comes on — how a worn electromagnetic clutch sounds and what a workshop checks.
• Alternator belt squeal: the causes Why a drive belt squeals: slack tension, wear, oil on the pulleys, idlers. How to find the cause from the moment the squeal appears.
• Alternator or water pump: telling the whine apart The alternator and the water pump sit on the same belt and whine alike. The checks that separate them in ten minutes and what each version risks.
• Alternator squeal: bearing or belt How to tell a slipping belt from a whining alternator bearing: the difference in sound, three tests without dismantling anything.
• An engine knock at idle Why an engine knocks at idle: hydraulic lifters, the timing chain, valves or the accessories. How to tell the causes apart by the sound.
• An engine knock only when cold: the full picture Why an engine knocks after starting and goes quiet as it warms: lifters, piston skirts, the chain, cam phasers. Where normal ends and bore scoring begins.
• An engine knock that goes away with warm-up Why an engine knocks when cold and goes quiet once warm: hydraulic lifters, piston slap, the chain tensioner. Where normal ends.
• An engine knock under load A knock under load: how to tell detonation from bearing knock, where the timing chain comes in, and when driving on becomes dangerous.
• An engine knock when hot Why an engine starts knocking after warming up: oil, hydraulic lifters, bearings or detonation. How to narrow the cause down by the behaviour of the sound.
• Backfiring through the intake: causes Backfiring into the intake manifold: a lean mixture, misfires, timing out of phase. How to find the cause and how it differs from banging out of the exhaust.
• Cam phaser rattle when cold Why cam phasers rattle for the first seconds after a cold start: a worn actuator, the OCV valve, the oil. How to check it yourself and what follows.
• Can you drive with a humming wheel bearing How far you can drive with a humming wheel bearing, what each stage of wear risks, how to reduce the risk on the road and how the repair is decided.
• Can you drive with a squealing belt A squealing accessory belt: how long you can drive, what a snapped belt risks, how to tell belt wear from an idler bearing and how the repair is decided.
• Can you drive with a stretched timing chain What a stretched timing chain risks, when driving to a workshop yourself is acceptable, when you need a tow truck, and what delay actually costs.
• Can you drive with a whining water pump A whining water pump means a worn bearing. What it risks on timing-belt and belt-driven engines, how to check it in five minutes and how the repair is decided.
• Can you drive with engine knock Which engine knocks let you drive to a workshop and which mean switching off and calling a tow truck. The rules of a gentle regime and what not to do.
• Checking engine mounts under load The load test for engine mounts: selecting gears against the brake, what movement to look for, and how to tell mounts from other knocks.
• Checking timing chain tension by ear How to hear a stretched timing chain: the conditions where it gives itself away, how it differs from lifters and injectors, and what a cold start shows.
• Chevrolet Cruze alternator bearing whine A whine under the bonnet of a Cruze that rises with revs: how to tell the alternator bearing from idlers, the water pump and the one-way pulley.
• Chinese SUVs: common noises on Chery, Haval and Geely Which noises show up most often on Chinese SUVs in their first years, what lies behind them and which check it makes sense to start from.
• Cold knock on a Škoda Rapid / Octavia 1.4 TSI Cold knocks on Škoda Rapid and Octavia with the 1.4 TSI: chain and tensioner, hydraulic lifters, accessories. How to tell them apart.
• Cold knock: timing chain or cam phasers A rattle in the first seconds after a cold start comes from both a stretched timing chain and the cam phasers. How to tell them apart by duration.
• CR-V all-wheel-drive coupling whine Whining from the rear coupling of a CR-V during tight turns and at low speed: why the fluid is usually to blame and how to tell it from a wheel bearing.
• Crackling when pressing the clutch Crackling as the clutch pedal goes down usually comes from the fork, the guide sleeve or a dry pivot. How to tell a cheap cause from a gearbox-out job.
• Diesel-like clatter: injectors or valve clearances A petrol engine has started clattering like a diesel: when the injectors are to blame, when it is valve clearances, and how to tell them apart by ear.
• Engine knock after an oil change Why an engine started knocking after an oil change: viscosity, level, filter, flushing. When the sound clears itself and when to go back.
• Engine knock: all the causes by type of sound A map of engine knocks by character of sound: ticking, clicking, ringing, dull thumps. What each one means and how urgent it is.
• Engine mount failure: the symptoms A jolt when pulling away, vibration at idle, a dull thump shifting from drive to reverse — how to recognise a failed engine mount and what it leads to.
• Engine or accessory knock: how to localise it A knock from the engine bay does not always come from the engine. A few checks separate the belt-driven accessories from the engine's own mechanics.
• Engine rattle at start-up Why an engine rattles at start-up: the starter, cam phasers, the chain tensioner or the alternator decoupler. How to tell them apart by the moment.
• Engine ticking at idle Why an engine ticks at idle: valves, hydraulic lifters, injectors, the timing chain. How to tell harmless ticking from the worrying kind.
• Engine ticking: dangerous or not Why an engine ticks: when it is normal injector operation and when it is worn hydraulic lifters or valves. How to tell a harmless sound from a serious one.
• Engine whine under acceleration Where a whine under acceleration comes from: the alternator, power steering pump, idlers, water pump or gearbox. Simple tests to find the source.
• EP6 balance shaft knock on Peugeot and Citroën What actually knocks in an EP6 engine when owners talk about balance shafts: the chain, the tensioner, the cam phasers and the oil. The checks.
• Ford Focus clutch fork knock Clicking and knocking as you press the clutch pedal on a Focus: how to check the fork and the release bearing, and what a workshop does.
• Fuel pump whine: normal or about to fail Where the line runs between an ordinary fuel pump hum and the whine of a dying one: which signs are harmless and which need a quick response.
• G4FC ticking on Solaris/Rio: normal or bore scoring The G4FC ticks at idle: where the standard injector chatter ends and a worrying sound begins. How to tell normal from scoring and what to check.
• Grinding noise when starting the engine Grinding when starting the engine: the starter pinion, the flywheel ring gear, the timing chain. How to find the source from when the sound occurs.
• Gudgeon pin knock: how to identify it How gudgeon pin knock sounds, how it differs from detonation and valve noise, which tests confirm it and what the repair involves.
• Gurgling in the engine after you switch off Gurgling after you switch off: when it is normal cool-down and when it is air in the system, a tired cap or a head gasket. Checks you can do in five minutes.
• Haldex coupling noise: the symptoms How a struggling Haldex coupling sounds, why the crunch appears during low-speed manoeuvres and how it differs from a CV joint clicking.
• How not to be upsold during a workshop diagnosis What an honest diagnosis includes, which phrases should make you ask a question, and how to check the work you have been quoted without knowing cars.
• How to check hydraulic lifters How to tell that hydraulic lifters are the source of the ticking: cold and warm tests, how they differ from valve clearances and injectors, and what to do.
• Hydraulic lifters ticking when cold: normal or not Why hydraulic lifters tick after a cold start, how many seconds of ticking counts as normal, and when it is time to change the oil or the lifters themselves.
• Hyundai/Kia bore scoring: how it sounds How to recognise cylinder bore scoring by ear on Hyundai and Kia engines: the character of the knock, its link to warm-up and load, and how it is confirmed.
• Is a cold knock that goes away dangerous A knock at a cold start that disappears after warm-up can be harmless or the warning of an expensive repair. How to tell them apart by timing and character.
• Metallic pinging in the engine under acceleration Pinging like coins in a tin under acceleration is usually detonation. The causes — fuel, carbon, plugs, knock sensor — the risk and what to check first.
• Mitsubishi 4B12 top-end noise: hydraulic lifters Ticking from the top of a 4B12: how hydraulic lifters behave, why the oil is usually to blame, and how the sound differs from the chain.
• Nissan Almera/Qashqai timing chain stretch symptoms How a stretched timing chain sounds on the Almera and Qashqai, how it differs from other engine knocks, and how the repair is decided.
• Nissan Qashqai cam phaser knock A short rattle at a cold start on a Qashqai often comes from the cam phaser. How to tell it from the timing chain and what a workshop checks.
• Noise underneath: exhaust or undertray Metallic rattling from below comes from either the exhaust system or the undertray. How to separate them by ear and by hand in ten minutes.
• Noises after an engine bay wash A squeal, a rattle or shaking at idle after washing the engine bay. Which noises clear by themselves in a couple of days and which mean a soaked part.
• Noises that mean stop driving now Most car noises can wait for a workshop, but a few mean switch it off now. The signals, how to stop safely and what to do once you have.
• Noises when starting in freezing weather Belt squeal, the knock of thick oil, starter grinding: the sounds of a cold start in frost. What counts as normal in winter and what needs a workshop.
• Pinking under acceleration: the causes Why an engine pinks under acceleration: detonation, fuel, carbon, spark plugs. How to tell harmless pinking from worn gudgeon pins.
• Rattling under the car when accelerating Heat shields, an exhaust touching the body, knocking or a broken catalytic converter: why a rattle appears under acceleration and how to tell harmless from serious.
• Rattling under the floor at speed Heat shields, the flexible section, exhaust hangers: why something rattles under the floor at speed, how to find the source and what it leads to if ignored.
• Recording a car noise for a mechanic How to record a car noise on a phone so it can actually be heard: where to hold the phone, what to say, which regimes to capture and what to avoid.
• Renault K4M hydraulic lifters: ticking when cold The K4M engine ticks on a cold start: how hydraulic lifters work, why they rattle, when an oil change is enough and when the lifters themselves need replacing.
• Signs of a burnt exhaust manifold gasket Ticking and hissing at a cold start, exhaust smell in the cabin, black soot at the joint — how to recognise a burnt exhaust manifold gasket.
• Signs of a burnt valve by ear Rhythmic popping in the exhaust, misfiring and hissing at idle: how to recognise a burnt valve by sound and which tests confirm the theory.
• Signs of a failing alternator decoupler pulley Why an alternator needs a decoupler pulley and how its wear sounds: a whistle at startup, rattling after shutdown, belt vibration. Checks you can do yourself.
• Signs of a failing timing chain tensioner How to tell a timing chain tensioner has weakened: clatter at a cold start, rustling at idle, a knock when blipping the throttle, and the risk of a jump.
• Signs of a failing VVT actuator Signs of a faulty VVT actuator: a rattle after starting, rough idle, higher consumption, P0010–P0017 codes. How to tell it from other noises.
• Signs of a failing water pump Coolant leaks, a whining bearing, pulley play and overheating: the signs of a dying water pump by stage, simple checks and what the replacement involves.
• Signs of a stretched timing chain How a stretched timing chain sounds, which fault codes it produces, how the stretch is measured without stripping the engine and how the job is decided.
• Signs of a worn alternator bearing How a worn alternator bearing sounds, how to check it without dismantling and how to tell it from idlers and the decoupler pulley.
• Signs of a worn clutch How to recognise clutch wear: slipping, a burning smell, a high pedal, jerking. A one-minute test, the stages of wear and how the job is decided.
• Signs of a worn idler pulley Whistling, whining and rustling from under the bonnet at idle often come from accessory belt idlers. How to tell an idler from the belt and the alternator.
• Signs of a worn timing belt How to tell a timing belt is worn: cracks, fraying, ticking and idler whine. Why a break is fatal for the engine and when the belt must be replaced.
• Signs of an intake air leak Hunting idle, whistling or hissing under the bonnet, a lean mixture and fuel trim codes — how to recognise an intake air leak and how workshops find it.
• Signs of big-end bearing knock How big-end bearing knock sounds, which signs come with it, what it is confused with and how the diagnosis is confirmed at a workshop.
• Signs of cylinder bore scoring Five signs of scored cylinder bores: a cold knock, oil consumption, lost power. Which engines are at risk, how the diagnosis is confirmed and what follows.
• Signs of engine detonation How to recognise engine detonation: pinging under acceleration, loss of power, rising fuel consumption. The causes, from fuel to carbon deposits.
• Signs of low oil pressure How to spot low oil pressure before serious damage: the warning light, lifter ticking, bearing knock. The causes of a pressure drop and how it is checked.
• Signs of main bearing knock A heavy low knock from the bottom of the block, falling oil pressure and vibration: how to recognise worn main bearings and how they differ from big ends.
• Signs of valve clatter How valve clatter sounds, why valve clearances drift, how it differs from other engine noises and what a clearance adjustment involves.
• Signs of worn engine mounts Vibration at idle, a jolt when selecting a gear, a knock under acceleration: how to recognise dead engine mounts and what decides the repair.
• Signs of worn timing belt idlers How worn timing idlers sound: rustling, whistling and hum from behind the cover. What a seized idler risks and how to tell it from accessory noise.
• Squealing after a belt change: why and what to do The belt was replaced but the squeal stayed or came back: tension errors, misalignment, idlers, decoupler pulley. How to find the cause.
• The engine misfires and knocks The engine shakes, the idle wanders and there is a knock: causes from plugs and coils to scored cylinders. How to find the dead cylinder and why waiting costs more.
• The noise stops when you press the clutch If a stray hum disappears when the clutch is pressed, the source is in the gearbox. How to narrow the list of suspects and what to check first.
• The starter chatters but will not crank The starter chatters but the engine does not turn: battery, terminals, solenoid. Simple checks on the spot and a table of causes.
• The starter clicks but will not crank Turning the key gives a click or a rapid chatter but the engine does not turn. What a single click and a rapid one mean, and how to tell battery from starter.
• Ticking injectors: normal or not Injector ticking: why it happens, when it is normal for an engine and when it signals a fault. How to tell it from hydraulic lifters.
• Ticking: valves or hydraulic lifters Ticking from under the rocker cover comes from both misadjusted valve clearances and worn hydraulic lifters. How to separate them by ear.
• Timing chain rustle: what it sounds like How a stretched timing chain sounds, when a rustle after starting is normal and when it means a workshop. The stages of wear and the risk of a jump.
• Top 10 noises you should not drive with Ten car noises after which driving on is unwise: what is breaking in each case and how to tell them from harmless sounds.
• Turbo whistle on diesel vans: Sprinter, Transit Turbo whistle on diesel Sprinter and Transit vans: where normal ends and an air leak or shaft wear begins, and how to check the hoses.
• Turbo whistle: normal or a fault When a turbocharger's whistle is a standard sound and when it signals a leak or wear: how to tell boost whistle from belt squeal and what to check first.
• What a stretched timing chain sounds like Rattle at a cold start, rustling from behind the cover, a change on lift-off — how to recognise a stretched timing chain and tell it from other knocks.
• What big end bearing knock sounds like A hard metallic knock from the middle of the block that grows under load: how worn big end bearings sound, how they are localised and what they threaten.
• What happens if you keep driving with noisy hydraulic lifters A ticking hydraulic lifter will not destroy an engine in a day, but it hammers the camshaft lobe and the valve. The scenarios, the timescales and what to check first.
• What to tell a mechanic: describing a noise properly How to describe a noise so a mechanic gets it first time: the five things that matter, wording that works, common mistakes and what not to say.
• Whining with the clutch pressed A whine that appears when you press the clutch pedal almost always means the release bearing. How to confirm it in a minute and what the repair involves.
• Why a petrol engine starts to sound like a diesel Why a petrol engine starts clattering like a diesel: valve clearances, a stretched timing chain, knocking, direct injection. What to check first, and in what order.

Other sections