We tried powerbraking. He said there was a lot of movement in the engine and suspected the rear motor mount...but, alas, no change after the mount was replaced. I'm thinking transmission as well...possibly differential....whatever causes the transmission to vibrate and make a constant exhaust-like noise while driving. It sounds like I'm pushing the engine too hard (like accelerating in neutral/park). I've also noticed, for example, when I get onto the highway from the on-ramp (or on a hill) if the car stays in the same gear too long, that if I press harder on the accelerator, the car won't respond(won't go faster, won't shift into the next gear), but if I take my foot off of the accelerator, it will shift into the next gear. | 
