I've got a 1997 Plymouth Grand Voyager (HD suspension, trailer towing
option, etc.) that does the same thing, no matter what kind of weather.
It's caused by friction between rubber or silicone bushings in the rear
suspension and the metal parts they touch. I can replicate the noise by
bouncing the rear end while it's parked. Handling, stability, etc. don't
seem to be affected, so I don't worry about it.
I've also got a 1998 Plymouth Grand Voyager (standard suspension) that's
got more than twice the mileage (105.5K) and has a very quiet rear
suspension. So let's make a leap of logic and assume that the stiffer
rear suspension pieces in the '97, especially the neoprene jounce
bumpers, are the culprit.
Unless you also hear metallic banging or scraping noises and have
handling problems, I wouldn't worry about the noise. However, prudence
suggests that a qualified suspension person should check out the rear
end, just to be sure.
You can try shooting some silicone lubricant at the potentially
offending parts (shock bushings, spring hangers, shock absorber
bushings, etc.) but I tried that with no success. I did get some relief
when I put some silicone grease on the frame contact points of the
jounce bumpers, but that didn't last. This indicates the white/yellow
neoprene bumper material causes noise when compressed that the standard
black rubber bumpers don't. YMMV.
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