Brickboarders, I need your help yet again. Thanks also to all who responded to my last query about my crapped out A/C compressor. By the way, if anybody has a good A/C compressor without a clutch, I'll buy it off ya :)

I've started to notice what appears to be a rev-based vibration in the vicinity of the right hand side of the passenger footwell of my '91 780 Turbo. I can cause the noise (which resonates throughout the frame of the car) to show up/go away by adding/removing throttle, depending on what speed I'm already at. It will show up occasionally everywhere from a dead standstill pulling out of my driveway to 80 mph on the freeway. It is also more likely to occur in slight left hand turns.

I suspect that I've got a motor mount or transmission mount or SOMETHING like that failing, and that is causing the exhaust downpipe on the turbo (right around where it bends from straight down to straight back) to contact the frame. The only other thing I think it could be is a cracked splash pan, but it's not cracked badly and I can't see anywhere that it might interfere with anything. At rest with the motor off, there is about .250" to .500" clearance between the downpipe and the frame, and I can see evidence where that undercoating goop or something like that has rubbed off.

Anyone experience this? And, if my theory about the motor mounts is correct, how difficult are they to replace?

Thanks in advance for your help and advice,

-Jon '91 Coupe 153K "Gustaf"