My neighbor has a garage full of muscle cars and plan to use his knowledge on the subject. He has a G8 as a daily driver(it's a beast) and he directed me to this website that has adjustable closed end J-pipe resonators that are tunable(4") being used on his car. Tunable meaning you can make the adjustment to whatever length is necessary so you can tune out the frequency(Hz) at the specific cruising RPM speed that has the bothersome drone.
http://www.g8board.com/forums/showthread.php?t=28454
