What that noise
probably is

A noise on its own tells us very little. A noise plus when it happens usually narrows it to two or three things before anybody has touched the car, which is why the first question is always about circumstances rather than sound.

When it happens matters most

Before trying to describe the sound, work out which of these it matches. It is worth more than any adjective.

• Only over bumps — suspension, almost always.
• Only while braking — brakes, and how urgent depends on the exact noise.
• Rises and falls with road speed — wheel bearings or tyres.
• Rises and falls with engine revs, parked — belt, pulley or something driven by them.
• Only on full lock — a driveshaft joint, usually the outer one.
• Only for the first minute from cold — often normal, occasionally a timing chain.

Knocking over bumps

By a wide margin the most common call we get, and by a wide margin the most over-diagnosed. Everybody assumes shock absorbers. It is usually not the shocks.

A light knock or clonk over speed bumps and potholes, worse at low speed, is typically a drop link — a small part connecting the anti-roll bar to the suspension. They are cheap, they are quick, and they are the first thing we check.

A heavier, duller thud, often with vague steering, points more towards a control arm bush. Worn shocks tend to produce float and bounce rather than a distinct knock, and they usually announce themselves by the car carrying on moving after a bump rather than settling.

Noises under braking

These are worth separating carefully, because two of them are routine and one is not.

• A high squeal that stops when you brake harder is usually the wear indicator doing its job. Book it in, but do not panic.
• A light squeal on a damp morning that clears after a few stops is surface rust on the discs. Entirely normal.
• A grinding or scraping that you can feel through the pedal means the pad material is gone and metal is meeting metal. That is a stop-driving noise.

A car that pulls to one side under braking is a different problem again, usually a sticking caliper, and it is worth sorting quickly because it wears one side out fast.

Noises that rise with speed

If the pitch tracks your road speed rather than your engine revs, you are looking at something turning with the wheels.

A droning hum that gets louder from about forty and changes when you steer gently left or right is a classic wheel bearing. Swinging the car slightly usually makes it louder one way and quieter the other, which also tells us which side it is.

An even hum that does not change with steering is more often tyre wear, particularly the sawtooth pattern that comes from an alignment problem. That one gets cheaper to fix the earlier it is caught, because the tyre can sometimes be saved.

Noises from the engine bay

Rev the engine while parked. If the noise follows the revs, it is being driven by the engine rather than the wheels.

A squeal on start-up that fades as things warm through is usually the auxiliary belt or its tensioner. A rhythmic ticking that rises with revs can be normal injector noise on a diesel, or it can be a timing chain starting to stretch, which is a much bigger conversation.

A rattle for the first two or three seconds from cold on a chain-driven engine is worth getting looked at sooner rather than later. It rarely gets better on its own, and the cost of catching it early against catching it late is not close.

The ones that mean stop

Most noises mean book something in. A few mean pull over somewhere safe.

1. Grinding you can feel through the brake pedal.
2. A loud knocking from deep in the engine that rises with revs.
3. Any new noise arriving alongside a red warning light.
4. A rhythmic slapping or flapping that matches wheel speed, which can be a tyre coming apart.

If you are unsure which category you are in, ring and describe it. That conversation costs nothing and takes less time than reading this page. If it turns out to need us, diagnostics comes to your address, and if it is brakes we can usually do it on the same visit.