I dropped off my car at the local dealership today because I had some rattling/creaking/clicking type noises coming from the rear passenger side. At first I thought it was the rear axle problem. However, the people at the dealership told me that my exhaust (not stock, Greddy evo 2) was hitting the under body brace. They improved it somewhat by replacing a missing bolt from the underbody panel. However they couldn't repair because they do not cover problems caused by aftermarket parts.

I've had this exhaust for 6 months and it never caused any annoyances. How would I go about fixing this issue?