Man, this is reallly buggin me because i cant tell where or what its coming from. When i COLD start my car, i dont know if you have noticed, but upon cold starting, the Rpms's go a little higher than a normal warm start. And i am only talking about the part when you turn the key and get the VROOM. During that Vroom, i get a really loud rattle that sounds exactly like a heat shield being loose. But it cant be a heat shield because i just had a brand new X pipe installed. (It did this sound before with the stock midpipe also but i assumed it was a heat shield). It only does in for a second or two during the Vroom part of any COLD start up. And never does it if you rev, or tap the throttle or warm start. I cant even pin point the sound, but it sounds like the bottom part of the engine, because i can hear it louder when its reflecting the sound off the ground than i can standing over the hood. Any suggestions??