A knocking or rumbling sound from the engine or exhaust can indicate serious mechanical issues. These noises often relate to worn or failing engine bearings, exhaust components, or internal engine damage. Because bearing knock is commonly associated with major engine wear, it should be diagnosed as soon as possible to prevent further damage and costly repairs.

What causes bearing knock noises?

Common causes of knocking noises from the engine or exhaust include:

• Worn or damaged crankshaft or connecting rod bearings
• Low or contaminated engine oil reducing lubrication
• Excessive engine wear due to high mileage or poor maintenance
• Loose or damaged exhaust components creating rattling or knocking sounds
• Detonation or pre-ignition (incorrect combustion inside cylinders)

Why do you need to fix knocking noises quickly?

Engine bearing knock is a serious warning sign. If ignored, it can lead to catastrophic engine failure where components seize, break, or throw a connecting rod. Driving with this issue risks complete engine damage and costly replacement. Early diagnosis can sometimes save the engine if caught in time.

How do you know when to get it checked?

Look out for these symptoms:

• Deep knocking or rumbling noise that increases with engine speed
• Knock occurs when accelerating or under load
• Low oil pressure warning light on the dashboard
• Exhaust rattles or metallic tapping noises

What happens during an assessment?

A mechanic will:

1. Listen to the engine at idle and under load to pinpoint the source of the noise
2. Check oil levels and condition, and test oil pressure
3. Inspect the exhaust system for loose or damaged parts
4. Perform diagnostic tests to determine if the noise is from engine bearings or another component
5. Advise whether repairs (such as bearing replacement or exhaust repairs) are possible, or if a major engine rebuild/replacement is required

How much does it cost to fix?

The cost varies widely depending on the cause. Minor exhaust repairs may cost $150–$400, but internal engine bearing failure often requires an engine rebuild or replacement costing $2,000–$6,000+. Accurate diagnosis is essential before repairs are quoted.

Is it unsafe to drive with a bearing knock?

Yes. Bearing knock is a sign of severe engine wear and can cause sudden engine seizure or breakdown while driving. If you hear these noises, it’s best to stop driving and have the car assessed immediately to avoid further damage and safety risks.