Today morning when I was in my car on the way to my office, I heard some unknown sound started all of a sudden, it sounds like thud thud thud. I think its from right part of the car under the bonnet. I am sure it wasn't there when I started driving this morning.

I parked my car for a while, kept engine running, opened up the bonnet and tried to find the issue but I cannot hear the sound. Quickly I checked some belts, pipes and other stuffs under the bonnet, also checked front wheels and checked all meters & lights on dashboard and found all well. As I started driving, again I was able to hear the sound.

I have already contacted my mechanic and have planned a visit coming Saturday. Hope nothing happens till then.

But I am curious, What can be the issue?

  • was it only specific to the right part of the bonnet? can you check if the serpentine belt(one connecting ac with engine) is tight? i mean it should not have any slack.
    – Shobin P
    Jul 22, 2015 at 9:18
  • I cannot confirm but I hear sound coming from right part. I have checked that belt, its not broken, and about its slacking, I just viewed it from distance, I have not checked its tightness. But by viewing it seems it is enough tight. However, I will look at it again later in the evening. Jul 22, 2015 at 9:38

1 Answer 1


Is this happening only when the car is moving?

Is it a cyclic event which happens faster as the vehicle moves faster?

If so, I'd suggest your right front tire has slipped a belt. This is something which happens internally to the tire. The tire would be made up of several belts which help the tire to roll smoothly. If one (or more) of the belts slip, it creates an out of round spot on your tire and produces the thumping sound you are hearing/feeling.

You can easily test this theory by moving the front tire to the rear position on the same side of the car (same process as rotating the tires). If the thumping then moves to the back of the car on that side, it has something to do with the tire and you should have it checked by a tire shop or your mechanic to verify.

The only way to fix this is tire replacement, though your tire may still be under warranty. This depends on how much wear is on the tire (how much tread is left on it). A slipped belt usually happens due to some kind of trauma to the tire, such as hitting a pot hole or a curb at just the right speed or direction.

  • Thanks Paulster2, I remember I drove my car right on to a half open manhole lid on the road at considerably high speed. I didn't felt it while inside my car and I neglected it. This may be the reason. Let me have it investigated. Jul 23, 2015 at 6:22

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