I got my exhaust change with the hks down pipe and hks mid pipe which is 2.75 inch and the perrin catdelete which is 3 inch. the problem that i am having is that i hear a knocking sound when i hit bumps. i had look at the exhaust and saw were the down pipe meets the cat it arch up a bit. the questons that trickle's me is did i but the right size catdelete or is there a little slant on the catdelete and i need to turn it around. also would longer hangers help. this is really bothering me guy, help me