What is the sound when releasing and stepping on the accelerator again?

[DelaneyLynn]

Releasing and stepping on the accelerator again produces a knocking sound from the engine. The professional term for this sound is "engine knocking". Causes: The main cause is carbon deposits on the top of the piston. These deposits form a highly intense hot surface, causing the fuel-air mixture in the combustion chamber to ignite spontaneously before the ignition stroke due to the carbon deposits. Although this combustion appears sufficient, it is spontaneous and premature, not occurring within the designated stroke, resulting in a metallic sound from the piston hitting the cylinder wall. Hazards: Engine knocking should be repaired promptly. Prolonged and severe knocking can lead to premature wear of cylinder components, significantly shortening the vehicle's service life.

[LeGage]

I've been driving for over a decade and often encounter this clicking sound when lifting and pressing the accelerator. Last week while helping a friend inspect an old Tiguan, we lifted it up and sure enough found play in the driveshaft universal joint - when metal components wear and the clearance increases, it produces similar knocking sounds. However, it could also be an issue with the CV joint, especially if the noise gets louder during turns. I remember once seeing a mechanic use a stethoscope to locate a resonant noise caused by loose screws on the engine underguard. Never delay fixing these loose chassis components - my neighbor ignored it last time and ended up having the driveshaft completely detach while driving.

[Dante]

Just a couple of days ago, I took my wife's Focus in for inspection—it was also making a clunking noise when accelerating after lifting off the throttle. The technician said it was caused by worn engine mounts. The cracked rubber allowed excessive engine movement, causing the metal brackets to collide and make noise when reapplying throttle. Additionally, damaged transmission mount bushings can produce similar symptoms, especially in manual transmission models. My uncle's Passat had an even more bizarre issue—it turned out to be a broken exhaust hanger, with the exhaust pipe swinging and hitting the underbody. I'd recommend focusing on checking these areas; using a pry bar to wiggle the components can help identify any looseness.

[BrantleyMarie]

I encountered a similar issue during my last road trip. There was a metallic scraping sound when I suddenly pressed the accelerator hard. The mechanic taught me a practical trick: have his apprentice listen outside the car while I repeatedly pressed and released the accelerator. It turned out to be excessive clearance in the turbocharger's connecting rod, causing impact sounds during pressure release. A friend who deals in used cars also reminded me that vehicles with modified exhaust systems are prone to this problem, especially when weld points crack. The negative pressure during sudden throttle release can make the metal sheets vibrate and produce noise.