I've noticed the noise before but, it suddenly got worse. Every time I drive over a speed bump or in perfection of the road it makes a thump sound in the back sounds like under the passenger seat area. I thought it must have been something in the trunk. So I cleared everything out and still happens. Sometimes I also hear it when I make a sharp turn, the handling seems to have been affected by it too. During sharp turns the rear goes looser than it usually does on a turn only sometimes. Any ideas guys? I checked my endlinks, since they did snap in half before. I replaced them with moogs and they've been fine. Rear ball joints? Rear struts failing?

Running stock suspension at the moment with Eibach Front and Rear Sway Bars, Neuspeed front upper strut bar

 

sounds like a blown shock since you ckd the obvious part

do the visual for oil traces from shock
do a bounce the corner several times and release test

 

I did the bounce the corner test it looks to respond okay, but from what I was reading the shock is supposed to rebound the car above its original height then settle down to its original height? I didn't do a visual yet since its been 100+ degrees outside. But I'm planing on doing that tomorrow.