TMans

I have this strange sound coming from the back of the car, specifically from the tire/wheel area. Not really sure how to describe it, but my friends said that it sounded like I had a flat tire (not loud, but it can be heard). I do not have a flat and everything looks fine visually so I don't know what is wrong.

My setup are 19 inch HREs on Toyo T1-S dropped on H&R springs, and the car is an '03 CLK500. This has been on my car for awhile now without any problems, but I know of two things that are a bit different now if it makes any difference. First, the car sits lower than usual in the back now (could be rubbing, but it doesn't seem like it). And second, the rear tire treads are wearing down.

Can anyone help me on this? Thanks.