What is the reason for the thumping sound when the car is running?
2 Answers
The reason for the thumping sound when the car is running is: If the sound changes with the vehicle speed and has a periodic rhythm, it is likely caused by abnormal noises from rotating components such as wheels or the drive shaft. It is important to thoroughly inspect the wheels, drive shaft, and other rotating parts for any abnormalities and to check if there is any interference with surrounding fixed components. The drive shaft is a high-speed rotating body with minimal support, so its dynamic balance is crucial. Typically, drive shafts undergo dynamic balance testing before leaving the factory and are adjusted on a balancing machine. For front-engine, rear-wheel-drive vehicles, the drive shaft transmits the rotation from the transmission to the differential. It can consist of multiple sections connected by universal joints.
I've experienced this thumping sound several times. The most common cause is a bulged or deformed tire. If there's a bulge on the tire sidewall, you'll hear a rhythmic knocking sound while driving. Another possibility is stones stuck in the tire tread, especially larger gravel pieces, which create a knocking sound with each tire rotation. An easily overlooked issue is wheel rim deformation. Last time when my wheel scraped against the curb, the steel rim got slightly bent, and I could hear a dull thumping sound when driving above 60 km/h. Otherwise, you should check the chassis. If the lower control arm bushings are cracked or the shock absorbers are leaking oil, you'll hear continuous thumping sounds when going over speed bumps. Never ignore this issue - last time I ignored the abnormal sound for three days, and the wheel nuts became loose, nearly causing an accident.
