Clunking noise when on throttle/off throttle in 2nd and 3rd gear
 

Guys, I'm wondering if anyone might be able to help diagnose the strange clunking noise that I'm hearing from the back of the car. It sounds like its' coming from the middle of the car somewhere under the rear sets or in front of the trunk; perhaps the rear diff?

In the last few days, I have noticed a pretty loud clunking noise whenever I'm in gear and let off the throttle. This is especially noticeable in 2nd gear, but can also be heard mildly in 3rd gear and sounds like a wrench knocking around in the trunk. I can't reproduce the sound when in neutral or with the clutch pushed in and have checked under the car for loose suspension parts just in case.

It sounds like the rear diff, but am wondering if anyone has experienced anything similar and can offer a diagnosis and/or fix.

Update. The issue turned out to be an incorrectly installed rear brake pad. I was swapping out my HP+ pads, which I use on the track for HPS and noticed that only half of the pad was worn, so there was no friction whatsoever on the other half of the pad. Once I swapped the pads out the clunking noise completely stopped.