V8 KETTLE DRUM NOISE

[Phil Williams <pmw0826@dreamscape.com>]

I did't realize how much I missed "Quattro" until I came upon what to
now appears to be an unsolvable problem.  I'm glad to be back!  My 1990
V8 develops a noise not unlike being in a kettle drum when sitting in
the back seat at any speed over 60mph.  Both rear wheel bearings have
been replaced and the drive shaft, together with the universal joint
have been replaced.  The noise is prominent with either my Michelin
X-Ones or my Nokias.  It also does not appear to related to the exhaust
system.  Air leaks have been almost ruled out for it doesn't matter if
the sunroof is open or closed and the one area where I had a door seal
problem, we corrected, and still the noise.  The noise is really only
noticeable in the back seat, but the solution of not having any back
seat passengers or drivers is not plausable.  I have not ruled out the
noise starting in the front since it there is a slight vibration felt in
the steering wheel (balance ok).  One of the front wheel bearings was
replaced, and the other is not noisy.  Any ideas would be greatly
appreciated.  My mechanic, Mike La Mark, at European Automotive Service,
in Utica, NY,  services more V8's than most, and does a great job, but
this has him stumped as well.  Thanks!