I believe its the upper perch, like bambrose stated. The part that has the 2 bolts that bolt to the frame, well, i believe in certain situations it is still able to rock from side to side. and ive asked about putting a thin rubber piece between the upper perch and car, and ive been told it would hurt the performance of the suspension. as of right now, im just dealing with it, its kind of grown on me and i dont notice it as much. but if you decide to experiment and find something out, make sure you post it on here. oh, dont bother sending it back to omnipower, its just a waste of shipping charges.