I just picked up my Phantom Black/Red M6 today...I LOVE IT. Now, this is the first LS1/M6 vehicle that I've owned...but I've driven my share of C5 M6's through work and never noticed the exhaust sound that I do on my GTO. As I accelerate and get to above 3k-4k RPM the exhaust sound changes from a nice rumble to a nice rumble with some burping or slapping noises. These noises go away as soon as I upshift and the RPM drops. Is that normal? Thanks for your help...I'm new to all this!