Knocking noise over bumps
A knock or clonk from one corner when the wheel drops into a hole or crosses a speed bump is play in a suspension joint - and the pitch tells you which one. A light, rattling tick over small ripples is almost always the anti-roll bar drop links or bushes; a deeper single clonk on bigger bumps is a ball joint, strut top mount or worn control arm bush; a knock that also appears when steering or braking is a tie rod end or strut mount. Confirm on a lift by levering each joint with a bar while a helper listens - visual inspection alone misses most of them.
Urgency
Visit a workshop soon
Possible causes, most likely first
- Worn anti-roll bar drop links or bushes
Light rattling knock over small bumps and cobbles, disappears when cornering as the bar is loaded. Grab the drop link and shake it, or lever the bar at the bushes; any free movement or a split rubber bush confirms it. - Worn strut top mount or bearing
Knock from the top of the strut tower on bumps and when turning the wheel at low speed, sometimes a creak. Open the bonnet, have a helper rock the steering and feel the mount for movement; check the rubber for separation and the bearing for notchiness. - Worn ball joint
Deeper clonk on bigger bumps, sometimes with vague steering. With the wheel lifted and the suspension unloaded as per the car's design, lever between the control arm and knuckle; more than about 1 mm of movement is excessive and a separated boot leaking grease is a warning sign. - Perished control arm bushes
Clonk under braking and on bumps, with the arm visibly moving in its bracket when the brakes are applied on a lift. Look for cracked, torn or oil-soaked rubber and hydraulic bushes that have leaked their fluid. - Worn shock absorber or loose shock mounting
Hollow knock on rebound and a floaty ride, oil weeping down the damper body, or a loose top nut. Push down each corner and release: more than one and a half oscillations means the damper is weak; check mounting bolts and bush collapse. - Broken coil spring
Sharp clunk, car sits lower on one corner and may rub the tyre on full lock. Inspect the spring coils, especially the lower seat where corrosion causes fractures; a broken spring must be replaced in pairs. - Loose or broken exhaust hanger or heat shield
Metallic rattle or bang from underneath on bumps that does not change with steering. Grab the exhaust and shake it with the engine cold; check each rubber hanger and tap the heat shields for looseness. - Worn tie rod end or steering rack bush
Knock over bumps that is also felt in the steering wheel, and play when rocking the wheel at 3 and 9 o'clock. Lever the tie rod end and watch for movement in the ball; check the rack moves in its mounting bushes when steering is rocked.
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What you can check yourself
- Note which corner the noise comes from and whether it happens on small ripples (anti-roll bar) or large bumps (ball joint, strut mount).
- Check if the knock also appears when turning the steering at standstill or when braking.
- Push down firmly on each corner of the car and listen for a clonk and watch how many times it bounces.
- Look under the car for a broken spring coil, a hanging exhaust or a loose heat shield.