Sorry about the all-caps... I could hear the bass-noise all day driving saturday but today I can't get it to reproduce. simple driving conditions, no hole in muffler or any external wierdness or road conditions... it's coming from the engine and it sounds like it's being transmitted through the bass in the speakers (which were turned off). I'll let you know tomorrow what the dealership says, thanks for the idea about the active noise suppression.
John