s13 chassis vibration above 65mph

[ZaK687]

So ive always had random clunking noises and vibration all throughout my s13 and over the past few years ive found the sources and eliminated them, but this one has me stumped.

I have good motor mounts and trans mount (trans mount may be a point of concern soon but my buddy has some new mounts for me that will be going in soon). I just swapped my old RSR cat back for a fujitsubo that sat closer to the chassis and after the swap I realized that my rear end clunk was the rsr exhaust swingin back and forth on worn mounts and slapping the subframe when turning at parking lot speeds. Now when ever I get up to 80 mph theres a loud and present vibration coming from the rear of the car that immediately stop if I go above 85 or drop back below 80. On top of this I also noticed a random vibration from somewhere below the rear quarter glass that shows up around 65mph and is constant at any speed above 65.

TLDR: Im trying to see if anyone has any ideas where these two vibrations are coming from/ being caused by. One that is very loud and from the rear specifically at 80 to 85 mph and another that shows up below the rear quarter glass around 65 mph and is present at any speed above that.

[z31andrew]

check your wheel bearings, and make sure your tires are balanced. Also make sure your subframe and all suspension components in the rear are tightened and torqued correctly. Lift up the back end of your car, and shake everything. Both rear wheels, grab the control arms and shake them, even take the wheel and hubs off and just check your bearings for any movement. Everything should be solid. Trans mounts or motor mounts wont have anything to do with it it's all suspension oriented.

Also if your car is on coilovers make sure the coils are not binding.

As for the one by the glass i would just rip apart your interior and find whats vibrating and insulate it.

My s13 has solid aluminum mounts and EVERYTHING vibrates, it's taking me some time to find all the vibrating spots but they are there and they can be fixed.

[ZaK687]

Update, turns out one of my rear wheel bearings was shot so it vibrated my car just right to get the strut bar to resonate. Still hunting down other small sounds, spraying the rear with 3M rubberized coating to see if that helps.