1800 rpm vibration solved!

["Sherry & Chuck Clark" <clark@rmi.net>]

Well I finally found that damn 1800 rpm harmonic vibration in
the 5k Tq over the weekend. I've recently replaced the two main
motor mounts and had the Prop shaft completely rebuilt. During this
time, I had removed many parts but never had any of the exhaust 
system removed or unbolted. I figured that I had jarred something loose
to cause this wierd vibration which could only be heard at exactly 1800
rpm and only with the car in motion. The noise could not be reproduced
with the car stationary and reving the motor. I had crawled under the car
twice and smacked, pushed and pulled on the exhaust system as I have
had my catalytic converter shield welded twice before due to it rattling loose.
Well guys and gals, the s.o.b. had worked itself loose for the third time in
3 years(the shield) If anyone remembers my post about 3 years ago, the first
shop I took it to(some hole in the wall) told me I needed a new converter from
Audi and it would only be $700!!!!!!! This was just for a loose shield AROUND the
cat. 
  Anyway, they ended up just welding the ends of the shield to the pipe and it
only stays put for about a year. Next time I'm going to have the shield removed
as I really don't generate alot of heat in the cat anyway(it somehow took a hike
3 years ago:-)) So to all the other listers with this same 1800 rpm vibration, please
check your cat. conv. shield when it's hot, using a tool-not your hand to see if there's
any movement or play. HTH,

Chad Clark '87 5k Tq