Hey Steve -
I fixed this on mine in the last couple of weeks. It
ain't completely perfect, but the payoff was well
worth the effort.
In my case, about 95% of the noise was from the bushings
which locate the rear sway/anti-roll/torsion bar.
Most of the rear suspension is mounted to the rear
subframe, which is isolated from the chassis by rubber
insulators. Not so with the rear sway bar. It mounts
directly to the chassis; hence any noise it generates
can be much more directly transmitted into the body.
To test, put the rear of the car up on jack stands.
Remove the rear wheels. Remove the 17mm nut which
secures the sway bar to the upper end of the sway
bar links. Do this on both sides and you can move
the sway bar by hand, simulating what occurs when
you drive over a speed bump, for example. Mine graunched
like crazy - it was amazing how much noise it made.
Repair is trivially simple. Remove the two 13mm bolts
which secure the bushing retainer in place. Pull
the bushing off the bar - it's split, so doesn't even
need to be slid off the end of the bar. Install new
busing - I used some silicone grease. Reinstall
retainer with 13mm bolts. Repeat for other side.
If it takes you an hour, you've had too many beers
I purchased a kit with two bushings & new 13mm bolts
for less than $5 mail order. In fact, I have a spare
kit, as I didn't realize one kit did the entire job...