I'm a new poster that needs some quick advice. Have a manual 04 coupe that has had a persistent rattle both in neutral and in gear when revved slightly (anything beyond 3k rpm masks the sound). It is especially apparant in enclosed areas like a parking garage. I've been bugging the dealer about this at 9k, 12, and 15k miles (every time I get an oil change) but no joy. I have now dug my heels in and am leaving it till fixed. They brought the area rep in to look at it, he replaced the left pipe, still no joy. Now the story I just got was that the rattle is inherent to many C5's and the correction is to replace the crossover exhaust pipe with an X crossover pipe from Borla, and that it is a standard warranty fix. I explained to the rep that I thought he was blowing smoke up my ass, but to go ahead and order the part while I researched the problem. Oh, by the way I would like to mention that I have owned a '97 and a '00 coupe as daily drivers as well, and never had an issue with the exhaust. I've seen some similar issues posted, but can anyone give me the educated gouge on this issue. Thanks--