After i got my invidia exhaust installed, i started to notice there were some sort of high pitch squeak noises came from underneath when driving over crappy roads. The high pitch squeaks were similar to the noises from a damaged springs. Try to jump on a 20 year old spring mattress, and you can get the feeling. Is it possible that the motor shop didn't installed my exhaust right? since the squeak is so distinctive, even the loud exhaust notes couldn't cover up it up, which really drove me crazy........

 

I'm guessing that the rubber exhaust hangers are rubbing on something thus making the noise.

I installed it fine and never notice any noise.

I would jack up the rear end and see if you can find the source of the noise. Shake the exhaust to see if it will produce the noise. I would also spray some WD-40 on the rubber exhaust hanger to see if that would help (I think there is 3 of them). Good luck!