[Phast SVX]

Well ever since i got my new exhuast installed ive been having problems with a loud rattle rising at around 2,700 and 3,000 rpm due to my heat shield rattling. Well i figured i would just have to tighten it down. Well turns out the the muffler is NOT touching the heat shield at all. Arghh.....This is the good slash bad part about my problem. The Flowmaster produces such a deep loud note that as soon as i hit a certain range, it cuases teh heat shield to resonate and rattle. I would really like to just remove it, as im not sure how big of arole it plays. IF its an important safety feature i will have to get around it, but removing it would be teh easiest way. Ive been told that my muffler will not last as long, but im not too worrried about that. Me and my friends 69 plymouth valient 318 has the same pipes as came with the car. So if anyone knows if it is a safety feature directly related to covering the gas tank(?) from the exhuast or somthing of the such please inform me. its really starting to annoying me. Oh yeah, after ive driven around for a while, and sometimes just out of the blue, it does not rattle.....