Did you put everything back together using a torque wrench?
Probably something is loose. shock cross-bolt is my first guess.
It is almost guaranteed that one of your suspension components is not tight enough. Go through every threaded fastener of your rear suspension and check it for proper torque. You will find it. Shocks bolts are the most likely problem area but it could be any component. I had a thump in my rear end and it was the adjustment sleeve of the adjustable panhard bar.
Yeah I mean I'm sure it's something suspension related, just don't know what to check next. I've been down there about a dozen times now just for the clunk. Initial install was with a torque wrench and the subsequent times I've tried torque wrenches and an impact gun (in case my torque wrench was off and I wasn't getting it tight enough).
If the clunking started when you put the shocks on the car, it's 99% probably the shocks.
It takes about 20 minutes to change shocks. You can drive the car without the shocks (I mean...don't drive it far though) to see if the shocks are the source of the noise, or you can put your stockers back on.
That's what I hoped it was but still clunking even with the stock shocks.