What Causes Engine Abnormal Noise After Releasing the Throttle?

[VanDaniella]

Possible causes of engine abnormal noise after releasing the throttle: aging or loosening of engine mounts, engine misfire noise, piston slap noise, etc. Aging or loosening of engine mounts: When these engine mounts age or become loose, the engine will vibrate, resulting in abnormal noise; Engine misfire noise: The exhaust gas flow from the vehicle will show obvious intermittency, accompanied by severe shaking of the exhaust pipe, and the abnormal noise from the engine can be clearly heard; Piston slap noise: Due to poor lubrication conditions and excessive wear of pistons and cylinder walls, the clearance tolerance between pistons and cylinder walls exceeds the normal range. During engine operation, the piston skirt impacts the cylinder wall, producing abnormal noise.

[LeBlakely]

I've experienced engine noises after releasing the throttle before, and it really scared me. The most common issue is belt problems, especially when the AC is on. When the tensioner pulley or belt ages, it tends to squeak when you let off the gas. Another possibility is a leaking exhaust pipe gasket—when you suddenly release the throttle, the airflow change can cause a popping sound. In my case, after a lot of troubleshooting, I found that the turbocharger's cooling pipe had come loose, causing metal pieces to vibrate and collide when I let off the gas. Additionally, if the engine mount rubber pads are worn out, the engine can drop slightly when you release the throttle, resulting in a clunking noise. I suggest carefully listening to identify the source of the noise, with special attention to the belt area and the exhaust system under the chassis. If you're unsure, take it to a repair shop ASAP—I ended up spending extra money last time because I waited too long.

[McSophie]

After driving for ten years, what I fear most is the sudden strange noises from the engine. Abnormal sounds when decelerating usually fall into a few common scenarios. Belt slippage is the most frequent issue, especially in older cars—insufficient tension can cause a squealing noise during sudden RPM changes. If the exhaust system gasket ages and leaks, the rapid pressure change when lifting off the throttle can produce a popping sound. Turbocharged car owners should be extra cautious; worn turbine blade bearings may create a metallic grinding noise when decelerating, which is downright painful to hear. Additionally, worn-out ball joint bushings in the chassis can cause a clicking sound, though this is usually more noticeable when driving over bumps. Just the other day, my neighbor's Audi had its turbo intercooler pipe come loose, producing a whistling noise every time he let off the gas. Get it checked ASAP—minor issues can snowball into major repairs if ignored.

[Pires]

I specifically consulted a seasoned mechanic about the abnormal noises when releasing the throttle. There are mainly two sound sources: a whooshing sound could indicate exhaust pipe leakage, especially at the gasket connections; while a squeaking noise is most likely caused by worn belts or tensioners - when aged rubber components experience RPM fluctuations during throttle release, they'll produce friction noises. Additionally, turbocharged vehicle owners should pay attention to the wastegate, as sticking valves may produce venting sounds. Remember these key diagnostic points: roll down windows to locate sound direction, test during both cold and warm engine states, and compare with neutral revving. If uncertain, never force the vehicle to operate - visiting a repair shop for inspection is the safest approach.