Why is my car making a knocking noise?
A knocking noise from the engine can range from minor to very serious depending on where it is coming from and when it occurs. A light knock on cold start that disappears when warm is often a hydraulic tappet. A deep metallic knock that gets worse under load (engine knocking or rod knock) is serious and means the engine has internal bearing damage — stop driving and investigate immediately.
Likely causes
Engine bearing wear (rod knock)
Deep metallic knock that worsens under acceleration — serious internal engine damage
Hydraulic tappet / lifter noise
Light ticking/knocking on cold start, usually disappears when warm after oil circulates
Piston slap
Light knock when cold, from worn piston-to-cylinder clearance, usually reduces when warm
Loose heat shield
Metallic rattling/knocking from exhaust area — often harmless but should be secured
Worn engine mount
Knock or clunk when accelerating or changing gear — engine rocks on worn mount
Repairs you may need
Typical cost range: £60–£2000 — Engine mount: £150–350. Tappet issues: £100–300. Internal engine damage (rod knock): £800–3,000+.
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