I have a 08 S4 and I took of the pipes to see what It would sound like with out them, I since have modified the pipes rewelded and other things but they sit just fine on the cats and the hangers line up as well. But now I have this clunking noise right underneath my arm rest and shifter and seat area. The cats are secure and the pipes are pretty solid aswell I just don't understand what It could be, if anyone could let me know their thoughts I would appreciate it.