i have a 96z with 90k and when i go over bumps i hear a thumping noise from the rear .my bump stops are dry rotted and falling apart and it seems like the rear of the car is sitting lower than it should.

 

Still running stock shocks, if so they're probably shot.

 

Sounds like a good time to start upgrading/replacing some of your worn out rear suspension components.

 

I dont think the shocks are stock,but who knows,i just got the car 6 months ago,they are white and thats all i know.they back end isnt all bouncy or anything.

 

One or both of your shocks have taken a dump. Just head to your auto parts store and grab some new ones. The rears are fairly cheap and easy to install on your own.

 

Doesn't sound like it, the factory shocks on the Z28 are orange DeCarbons. I know the KYBs are a white housing shock, but I'm sure there could be other replacements on the market as well in the same color so that is purely a guess.

 

I'm kind of in the same boat as you are, 96z with 105K miles. My lower control arm were totally shot and making a terrible groaning noise when I went over bumps or into my driveway. When I replaced them with the J&M ones, the noise went away. I know my shocks are original and they are shot so they will be replaced shortly. My bump stops are also shot so at some point I'll be looking for replacements. While I was at it I also replaced my bushings and end links on my rear stabilizer bar, they had pretty much had it also. I will send a report when I get my shocks and phb replaced. I'm hoping for some definite improvement.

 

My 95 Formula has about 95K and at around 90K it started to get the same noise. I replaced the shock back at about 30 to 35K with SLP take-off's many years ago. The rest of the suspension is all aftermarket. SFC, 1LE springs, control arms, etc.... I just ordered new blisten rear HD shocks, when they get in I'll let you know if it fixed the problem. I checked everything and can't find anything loose with the suspension, rear tire, jack, speakers, etc... Almost sounds like the rear window is loose, but it's fine. The noise is driving me crazy. My 91 Formula 350 made the same noise around 90K and I couldnt figure it out then. I just sold it.

JCS

 

Might be the rear hatch bouncing around.

 

Could be. That happened to me, there is an adjustment on the stops to cure that problem. I've got one that has me stumped-I get a clunk after sitting a while. I'm pretty sure that the wheel rolls too far for it to be a sticking brake pad. I had a clunk going over bumps that was trailing arm bushings that were too loose as well but this sounds different.

 

panhard bar!it was that damn panhard bar.i feel like a retard

 

Checked the stops for the rear hatch. No problem there. Replaced the shocks in the rear with Bilstein HD's. Problem mostly solved. The noise is pretty much gone, but I still hear it on hard bumps. Could it be coming from the front as well, but still sound like its coming from the rear?
Would it be worth it to replace the front shocks and also put new shock mounts in as well?

 

What do you mean by it was the panhard rod? Is it broken or are the bolts just loose? How did you fix it?

 

if you have cat back exhaust check that. i had a thump/clunk and it was a loose hanger