Knocking sound from back end
Ok so I just bought a 2006 GTO, 6 spd manual, car has 77k miles on it. A couple days ago I was leaving work and driving through town I noticed a fairly loud knocking sound coming from the back end. If I stayed in the gas just enough to keep the car rolling smoothly, it would go away, but as soon as I let out of it, or started to pull a little, it would come back. It's a constant knock, not just a single clunk like you usually hear. The sound was similar to a broken connecting rod in an engine, just slower.
So being a mechanic, I headed back to where I work so I could get the car on a lift and see if I could find out what was going on. Got it lifted up, spun the rear wheels a couple times and I heard the sound twice and then it went away, so I couldn't really get a definite pin point on it. I checked everything out back there just to be sure, couldn't find anything out of the ordinary. Diff felt nice and tight, axles felt fine, all suspension felt good. I haven't pulled the cover off the diff, don't really want to if I don't have to.
I have driven the car a good 150 miles since and haven't heard the noise again. It's just worrying me and I don't have the time to really dig into it. Not to mention I haven't ever heard anything like it.
Has anyone ever experienced something like this?