Causes of Engine Tapping Noise

[Drew]

The excessively loud "tapping" sound from a car engine requires focused inspection of the following aspects: 1. Many new car owners, after their first warranty maintenance service, may suspect abnormal engine noises when inspecting under the hood at idle speed (since prior to maintenance, they operated from the cabin and couldn't hear the normal tapping sound of the engine below the hood. Now, hearing this sound occurs specifically during idle with the hood open while listening for engine noises, which naturally allows hearing normal engine operation sounds.) If this sound isn't audible inside the car, it's generally not significant—typically originating from the valves or fuel injectors. The carbon canister purge valve can also produce this sound, but it's crisper. A distinguishing method is to slightly rev the engine at idle and observe if the frequency changes. If unchanged, it's likely the electromagnetic valve; if it varies, it's probably valve-related. If barely audible inside the car, it's usually not a major issue—vehicles normally have corresponding tapping sounds from injector operation or valve mechanisms. Another similar sound comes from the timing chain, though it's more of a rattling noise than tapping. 2. Most cars exhibit slightly louder engine sounds during cold starts compared to warmed-up operation. As long as the sound is even and smooth without harshness, it's generally normal. This occurs because cold conditions leave piston-to-cylinder wall gaps suboptimal and oil lubrication incomplete. Typically, when engine block temperature reaches about 95°C, sounds normalize. 3. Oil-related factors. Using substandard oil, prolonged intervals between oil changes, or low oil levels can increase friction between valves and guides or hydraulic lifters, amplifying various engine noises. 4. If concerns persist after these checks, visiting a nearby 4S shop or auto repair facility for professional diagnosis is recommended to identify the fault.