what is this loud sound underneath the rear of my car when I drive ? on 1993 BMW 325i

the faster I drive the louder it gets

Get Your Car Fixed at a RepairPal Certified Shop.
We certify shops based on expertise, quality work, and verified customer reviews
1 answer
Bad tire wear (cupping on inside tread?). Rub your hand over the tread in the direction of rotation and see if it has high/low spots.