What is the reason for the thumping sound when the car is running?

[WillowMarie]

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.

[DeSkylar]

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.

[JuliaAnn]

I'm a regular at the auto repair shop, and this kind of abnormal noise mostly comes from the chassis or tires. First, pay attention to the frequency of the sound. If it's synchronized with the vehicle speed, it might be a problem with the wheel hub or tires, such as a deformed or out-of-round wheel hub or a bulging tire. If the noise gets worse when turning the steering wheel, it's likely due to a loose tie rod end or issues with the suspension control arm. Additionally, if the driveshaft universal joint is worn, rear-wheel-drive cars will produce a dull thumping sound when accelerating. I recommend checking these areas immediately: look for bulges or deformities on the tire surface, scratches or deformities on the wheel hub, loose chassis bolts, and whether the driveshaft boot is torn or leaking oil. Don’t end up like my cousin, who regretted it only after the suspension bolts came loose while driving on the highway.

[LaBrooklyn]

From experience, the thumping sound is most likely a tire issue. Last time, my tire had a bulge on the sidewall, and it felt like a hammer hitting the chassis when driving—the faster I went, the more noticeable it became. Pebbles stuck in tire treads can also cause this, especially after driving on gravel roads; when pebbles get lodged in the drainage grooves, they create a tapping sound. Another often-overlooked issue is the detachment of balancing weights on the inner side of the wheel hub. When the wheel spins at high speed and loses balance, the entire car body will shake. I recommend first checking the tires for any external damage or foreign objects stuck in the treads. If that doesn’t help, get a wheel balance check. Problems with the chassis suspension can also cause thumping noises—my neighbor’s car had worn-out stabilizer bar bushings, making it sound like a drum when driving.

[DeParker]

Don't panic when you hear a thumping noise. It could be a tire issue, like tread bulging or large stones stuck in the tread, especially noticeable at 40-60 km/h. It might also be loose chassis components – once my anti-roll bar link came loose after hitting a pothole, making a thump with every bump. More seriously, it could be wheel deformation, which is truly dangerous. My colleague's alloy wheel hit a curb, causing the whole car to shake at highway speeds. I recommend pulling over first and walking around the car to check for abnormal tire bulges. If you must continue driving, avoid rough roads and proceed slowly directly to a repair shop. Don't be like me – I thought it was just items rolling in the trunk, but it turned out my wheel bolts had loosened by five full turns.

[Lucian]

The knocking sound needs to be judged case by case. If it occurs within a specific speed range, such as being particularly noticeable between 60-80 km/h, it's mostly due to failed tire dynamic balance or slight wheel rim deformation, causing vibration from centrifugal force during high-speed rotation. If accompanied by steering wheel shaking, then it's an issue with the front wheels. If the sound comes from the rear of the car, rear-wheel-drive vehicles should check the driveshaft universal joint, while front-wheel-drive vehicles should inspect if the brake discs are deformed. Another possibility is the aging of exhaust pipe hangers; when the exhaust pipe becomes loose, it may knock against the chassis when going over bumps. From my personal experience, the sound was caused by a tire bulge—before replacing the tire, it sounded like someone was hitting the fuel tank with a stick. It's recommended to conduct a comprehensive inspection as soon as possible to rule out potential hazards.