Thumping Sound While Driving

I have a 2001 GP and about a month ago while drving on the highway I started hearing a thumping noise from the bottom of the car. Couldn't really tell if it was coming from the front or the back. I needed new tires on the front so I figured I would replace those and see what would happen. Got the from replaced and still same noise. It does it on all different roads, smooth, or rough. I am thinking that it may be the back tires but they are not ready to be replaced. I have a feeling that it is something with the tires because as I drive faster the thumping gets faster and when I slow down it of course gets slower.

Sounds like a busted belt in one of the rear tires. Get the car up on a jack or lift and rotate the tire. As the tire is rotating, run your hand along the tread face and you should feel and maybe even clearly see the ridge forming the end of where the busted belt is at. The other possibility is one of the tires is out of balance, but I would look for the busted steel belt first. Good luck.

I agree with GPFred, something is more than likely wrong with your rear tires. I also have a 2001 GP and I think that the factory screwed up on the way the rear tires are aligned. I've noticed on a lot of GP's that if you look at the rear of the car, the tires are tilted in on the top, and out on the bottom, causing the tire to wear on the inside edge. I would suggest getting new rear tires and a four-wheel alignment, and it should solve your problem.

Check for a bent rim. I hear a thumping sound like you described because the inside of my left rear rim is bent.