Recently my exhaust has started to sound a bit metallic and rattly at certain rpm's. I think I blew out my catback. I checked under the car and all the heat shields are tight. There are no exhaust leaks either. The sound seams to be comming right out of the exhaust tip. The exhaust is a Greddy SP that I bought used so its a few years old. Worked great for a year but seams to have gotten louder lately. Maybe it sthe single turbo? Any way I can check for sure before I dump a ton of cash on a new catback?