An exhaust does not get louder suddenly and for no reason: if the car has started sounding deeper, a leak has appeared somewhere in the system — the gases are escaping before the silencer, bypassing its baffles. Sometimes that is a micro-crack at a joint, sometimes a hole burnt right through a box. The good news is that the source is nearly always found in ten minutes on a lift, and some of the causes are cheap to cure. Here are the typical leak points, their sound signatures and what decides the repair.
Where leaks usually appear
- The silencer and resonator. The boxes rot from the inside through condensation and from the outside through road salt. A burn-through along a seam or the floor of the box gives a deep rumble, noticeable at idle and rising with the revs — signs of a rotten silencer.
- The flex pipe. The flexible corrugated section between the engine and the pipe. A torn flex hisses and roars, the sound growing under load, often audible from under the bonnet — signs of a torn exhaust flex pipe.
- Joints and gaskets. Flange connections after the catalytic converter and between boxes lose their seal through burnt gaskets and seized studs — the sound is sharp and cutting.
- The exhaust manifold gasket. A leak right at the engine: chattering and roaring from above, louder when cold — that case is covered in detail in the exhaust roars when cold and burnt exhaust manifold gasket signs.
- A cracked downpipe. Often near the flex or a mounting: the metal tires from vibration, especially with tired engine mounts.
A separate signal is popping and banging in the system on lift-off. That is a different mechanism — fuel burning in the pipe — and it is covered on the symptom page exhaust backfire.
The sound of a leak and its location
| How it sounds | When it is louder | Likely location |
|---|---|---|
| Deep rumble, a “sports exhaust” note | In all states, rising with revs | Burnt-through silencer or resonator |
| Hissing with a roar | Under load, on acceleration | Flex pipe, cracked downpipe |
| Sharp cutting hiss | Audible at the floor at idle | Flange, joint gasket |
| Chattering from above, louder when cold | First minutes after starting | Exhaust manifold gasket |
| Metallic rattle on top of the rumble | Over bumps and on acceleration | Broken hanger, pipe touching |
If the volume grew at the same time as a rattle over bumps, do not blame it all on the exhaust: a pipe sagging on torn hangers knocks against the body, and the running gear gives similar sounds — compare the picture on the page rattling under the car and in noise underneath: exhaust or undertray. Front suspension knocks have their own causes, from anti-roll bar links to the arm joint covered in signs of a worn ball joint.
Judging the scale yourself
First, an inspection on a cold car. Go along the system with a torch: rusty crumbs on the boxes, black sooty marks at the joints (gases always leave soot where they escape), damp patches of condensation at a seam. Soot is an almost guaranteed marker of a leak, and it can often be found without a pit, just by looking underneath with a light.
Second, the palm test. With the engine running and cold, briefly block the tailpipe with a thick glove for a couple of seconds: with a sealed system the pressure pushes noticeably against your palm, with a large leak it barely does, while the hiss from the hole gets stronger.
Third, listen to the pattern. A leak ahead of the silencer makes the sound louder under load; a leak in the box itself gives an even rumble in all states. Those observations are worth writing down and telling the mechanic — they save time on the lift.
Extending the life of the exhaust system
Every exhaust rots, but the speed of the process is controllable. The main killer of the system is condensation: water collects in the boxes on every journey, and if the route is short it does not have time to evaporate. A car living on ten-minute commutes benefits from a regular half-hour run at speed — the system heats right through and dries out.
The second factor is road chemicals. Salt eats the boxes from outside, so washing the underside after winter is prevention rather than cosmetics. The third is mechanical: intact rubber hangers stop the pipe vibrating and cracking at the welds, and care over kerbs and deep ruts saves the boxes from dents, which is where corrosion often starts. None of that costs anything comparable to a new silencer.
How the repair is decided
The criterion is the state of the metal around the hole, not the hole itself. A single burn-through in a sound box is welded; a box thinning along its seams is replaced, because a patch on tired metal lasts months. Ask to be shown the surrounding wall rather than the hole — that is the one thing that decides between a cheap fix and a repeat visit.
Two things mechanics do not always say. If a joint is opened, the gasket and the studs go back new: seized studs snap on removal, and a joint reassembled on old hardware leaks again within weeks. And a burn-through close to the catalytic converter also upsets the oxygen sensor readings, so fuel consumption rises — which means the sooner the leak is closed, the cheaper the whole thing, including the fuel.
Not sure it is the exhaust that has changed its voice? Record the running car in the Pro-Stuk app: it matches the recording with your answers about when the sound is louder and shows the likely causes with a level of urgency — which makes it easier to choose a workshop and not overpay for the search.
