I recently installed some godspeed lowering springs in the rear. I had previously done the same with some cheap eBay ones awhile back but there was a loud clunk going over even the smallest of bumps. I thought it was the cheap nature of the springs so I bought some higher quality springs. After installing the new ones the same problem occurred. I tried the springs with both OEM shocks and aftermarket ones and the problem seizes to go away. I tried trimming the bump stop as well. The clunking goes away after raising the car back onto OEM springs. All the Bolts are tightened to spec aswell. I raised the tires with a jack to see if it was a clearance issue but everything cleared and the shocks never bottomed out. Any Ideas

 

Did you replace the gasket that is between the shock mount and the body? That can be a source of noise. Another item I found in my searching when try to excise my Z of all suspension noise was that the lower shock bolt/mount in the rear "could" allow for movement and noise. Some people have added a bushing to the shock mount hole that the threaded side of the bolt passes through in order to eliminate/reduce the possibility of play there. There's a lot to search and learn here in the forums on suspension noises that might help, too.

 

Sounds like upper shock mounts. You can't see the failure but the bushings in the mounts wear and tear over time. Especially pronounced with stiff springs. BTDT at least 3-4x.

https://www.z1motorsports.com/rear-s...oaAlRwEALw_wcB

Or other sources for cheaper than OE.

 

+1 on the upper shock mount bushings. I forgot about that. I used the KYB ones and it got rid of my rear clunk.