Suspension knock is a distinctive, sharp sound, usually a single clunk or a rhythmic knocking as you drive over an uneven surface — distinct from a lighter rattle or clank underneath that doesn't move with the suspension. If the clunk happens when pulling away from a stop rather than over bumps, see our guide to a clunk when pulling away instead. It's caused by a joint or bush that's supposed to be tight and controlled becoming loose enough to move and make contact with something.
The most common causes
1. Worn anti-roll bar links (most common cause)
Anti-roll bar links, also called drop links, are small ball-and-socket joints connecting the anti-roll bar to the suspension on each side. Over time these joints wear and develop play, and poor road surfaces accelerate this. The result is a distinctive knocking, usually most noticeable at low speed over bumps or potholes. This is genuinely one of the cheapest and most common suspension repairs, so it's worth ruling out first. Vans carrying regular loads wear these out faster than most cars — see our guide for van drivers and trades on planning repairs around downtime.
2. Worn anti-roll bar bushes
Similar in symptom to the links, but this time it's the rubber bushes that mount the anti-roll bar to the chassis that have perished or worn. This can also cause a looser, more wandering feel to the steering, particularly when cornering.
3. Worn top mount bearings
The strut or shock absorber assembly rotates on a bearing at the top. When this wears or breaks, it can produce a similar knocking sound over bumps, and is sometimes mistaken for an anti-roll bar issue.
4. Worn suspension bushes or ball joints
Suspension arms attach to the car body via rubber bushings, and the arms connect to the wheel hub via ball joints. When either wears down, the resulting play can allow metal-to-metal contact, causing a knock, especially noticeable when turning or over rough surfaces.
Is it safe to keep driving?
Probably fine for nowA faint, occasional knock only over larger bumps, with no change to how the car handles. Get it checked at your next convenient opportunity.
Book it in soonA consistent knock on most bumps, or a looser feel when cornering. Book this in within the next couple of weeks.
Don't delayA loud clunk accompanied by noticeably reduced steering precision or stability. Get this checked promptly, as it could affect vehicle control.
What it typically costs to fix in the UK
| Likely job | Typical UK cost |
|---|---|
| Anti-roll bar drop links (per pair) | £60 – £190 |
| Anti-roll bar bushes | £80 – £180 |
| Suspension arm or bush replacement | £130 – £300+ |
Ranges compiled from Bumper, Checkatrade and ClickMechanic UK pricing guides, 2025-2026. Your actual quote depends on your specific vehicle and garage.
Frequently asked questions
Is it safe to drive with a knocking suspension noise?
A mild, occasional knock over bumps is usually not an emergency, but it shouldn't be ignored indefinitely, since worn suspension components affect handling and can wear tyres unevenly. If the knock is loud, constant, or accompanied by a looser or less stable feel when cornering, get it checked promptly.
What's the difference between anti-roll bar links and bushes?
Anti-roll bar links (drop links) are small ball-and-socket joints connecting the anti-roll bar to the suspension, and are one of the cheapest and most common causes of a knocking sound. Bushes are rubber components at various suspension pivot points that can also wear and knock, but usually cost a bit more to replace due to additional labour.
How much does it cost to fix a suspension knock in the UK?
Anti-roll bar drop links, the most common cause, typically cost £60 to £190 to replace including labour. Anti-roll bar bushes are similar, around £80 to £180. More involved suspension arm or bush replacement can cost more depending on the component.
Wondering if you should still be driving on this? See Is knocking over bumps dangerous?
For other noises, see all car noise guides.
Not sure what's causing it?
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Try MechdThis guide is for general information only and isn't a substitute for a qualified mechanic's inspection. Worn suspension components can affect handling and vehicle control, so have persistent knocking checked rather than ignored.