Why is my car making a knocking noise?
A knocking noise is most often worn suspension, brakes or a driveshaft joint, and the clue is when you hear it. Knocking over bumps points to suspension, knocking when braking to the brakes, a knock or click on tight turns to a CV joint, and a deep knock from the engine that rises with the revs should be checked immediately. Any knock that comes with poor handling, a warning light or a burning smell means you should stop driving and have it looked at.
A new knock or clunk from your car is easy to worry about, but the noise itself is a useful clue. Most knocking comes from a short list of parts, and the single best guide to which one is when you hear it. This guide runs through the common causes by symptom, so you can narrow it down, describe it clearly to a garage and know when a knock means stop driving.
Knocking over bumps
A knock or clunk as you go over bumps and potholes almost always points to the suspension. Worn drop links, tired bushes, a failing shock absorber or a loose component will knock as the suspension moves. These parts wear slowly and often show up first as an MOT advisory, so it is worth acting while the fix is small. Left alone, worn suspension affects how the car handles and can turn into a failure.
Knocking when you brake
If the knock appears as you press the brake, look at the brakes themselves. Pads at the very end of their life, worn or warped discs, or a sticking calliper can all knock or clatter under braking. Because this is a safety system, do not leave it. Our guide on brake warning signs explains the noises and feelings that mean your brakes need attention now.
A click or knock on tight turns
A rhythmic clicking or knocking that appears only on tight, slow turns, the kind of thing you hear manoeuvring in a car park, is the classic sign of a worn constant velocity joint on a driveshaft. It does not repair itself and gradually gets worse until the joint fails, so it is one to book in promptly rather than ignore.
A knock from the engine
A deeper knock that seems to come from the engine and rises and falls with the revs is the one to take most seriously. It can indicate internal wear, and continuing to drive risks turning a repair into a much bigger bill. If the knock is accompanied by a warning light, a loss of power or any burning smell, stop driving and have the car recovered to a garage. Our guides on the engine management light and a car losing power cover the related symptoms.
When accelerating or setting off
A knock or clunk as you pull away or accelerate can be worn engine or gearbox mounts, which let the engine move more than it should, or a driveshaft issue. It is usually less urgent than an engine knock, but it will not cure itself and is worth a look before it worsens.
What to do next
Note exactly when the knock happens, how fast you are going and what you are doing at the time, then let a garage trace it. A short diagnostic check is far cheaper than replacing parts on guesswork, and a good garage will confirm the cause and give you a written quote before doing any work. If the knock comes with poor handling, a warning light or a burning smell, treat it as urgent and stop driving.
The bottom line
Use the timing of the knock to point you at the cause, and get anything to do with the brakes, the steering or the engine checked quickly. You can compare local garages near you, see their ratings and opening hours, and send a booking request in about a minute. You pay the garage directly and there is no booking fee.
Key takeaways
- When you hear the knock is the biggest clue to the cause.
- Over bumps usually means suspension or something loose.
- A knock when braking points at pads, discs or callipers.
- A knock or click on tight turns is often a worn CV joint.
- A deep engine knock that grows with the revs is urgent.
- A diagnostic check pinpoints it before you pay for parts.
Frequently asked questions
Is it safe to drive with a knocking noise?
It depends on the cause. A light knock over bumps should be checked soon but is rarely an emergency, while a deep engine knock, a knock with poor handling, or a knock with a warning light means you should stop driving and get it inspected. When in doubt, do not risk it.
Why does my car knock when I go over bumps?
A knock over bumps usually comes from the suspension: worn drop links, bushes, shock absorbers or a loose component. These parts wear gradually and are common MOT advisories, so it is worth having them checked before they fail.
Why does my car knock when I brake?
Knocking under braking often means worn or loose brake components: pads at the end of their life, worn discs, or a sticking calliper. Because this affects your ability to stop, get it looked at quickly rather than leaving it.
What is that clicking or knocking when I turn?
A rhythmic click or knock on tight, slow turns, such as a car park manoeuvre, is a classic sign of a worn constant velocity joint on a driveshaft. It will not fix itself and gets worse, so book a check before the joint fails completely.
How much does it cost to diagnose a knocking noise?
A diagnostic check to trace the noise is usually modest, and it saves money overall by identifying the exact part rather than replacing things on guesswork. Ask the garage to confirm the cause and give a written quote before any work.