[VoltFish]

Tonight I noticed that there is a strange sound coming from the rear of the car. I can only hear it with the window down and it seems to be coming from somewhere around the back tire but it's hard for me to tell while driving. The sound is variable with speed and sounds like it could be something with the tire but I haven't found anything yet. The best way I can describe the sound is if you took a rubber flip-flop style shoe and were tapping the sole on the ground over and over and increasing in frequency with speed. Any easy answers for what this could be?

 

[bentbiker]

Jack up that corner of the car and spin the wheel by hand. If you don't hear anything, that points strongly at the tire itself. If you can't see anything wrong with the tire -- a bulge, something stuck in the tread, a belt separation, etc, stop at a tire shop and ask them to look at it; most will do that free. Discount/America's Tire will even repair it free, if it's repairable. You are at risk of a catastrophic tire failure, so take it seriously.

 

[Loboc]

It's probably a tire. It could be any tire. Sound source is very difficult to locate in a moving car. Taking it to a tire shop is good advice.

 

[ClarksonCote]

Usually that kind of sound is a small rock stuck in the tire treads.

 

[quirkySquirt]

Ditto on the small rock. The frequency of the sound will depend on how big a rock you have stuck and what you drive over. If the sound changes based on your driving surface, it's probably a rock.

Ditto on Discount Tire. I have had 3 nails repaired by them for free. They also get my business so long as the price delta between them and Tire rack is no more than $20 per tire/wheel/combo.

 

[VoltFish]

Thanks... Just as suggested I found a rock wedged in between the treads on the back left wheel. Popped it out with a key and the sound seems to have gone away.