Recently I installed my Ksport Kontrol Pro Coils and ever since only my passenger side rear makes a clunk anytime I hit a bump. I've jacked the car up and everything seems find, bump stops are fine and the spring isn't showing signs of anything wrong and the shock looks just fine. They're set to the stiffest setting so I'm not sure if that's it, this is my first experience with a lowered vehicle so I'm extremely unexperienced. Does anyone have any ideas or suggestions?

2009 Cobalt SS

 

If you have an exhaust on it then it may be the exhaust smacking the rear axle. Had that issue with mine when I put new lowering springs on. Wrapped a worm hose clamp around the hanger by the rear axle and tightened the living crap out of it so it would hit anymore, or at least as often

 

Looking at the exhaust is a good idea. I would also look at the rear axle beam bushings.