many omni's have this problem I have found. One of mine does it, I took everything back apart and inspected it and everythign is good, what I concluded is that because there is no rubber stopper above the upper plate, sometimes on certain cars, the upperplate can rock side to side if it doesn't sit completely flush. You know how it is only held in by 2 nuts, well I think it rocks side to side, perpendicular to those two nuts