Also worth checking:
If it's lowered check that it isn't the exhaust making contact with the rear beam. Lowering the car brings the beam closer to the exhaust where it kicks up and over. The rear hangers for the exhaust weaken and stretch over time which causes the exhaust to hang lower. With the car on the ground stick you arm under the car and follow the exhaust up and over the beam if you find you can only fit a finger or two between the exhaust pipe and beam they will be making contact over everything bump.