I've looked around the forums and internet for an answer to this question, but haven't found one yet. I'm hoping someone here can get me going in the right direction, or even share stories of their own that'll help me out.

I have a 2001 Volvo v70 XC with 107k on it. The transmission has been replaced recently, and I just had some work done on the rear drive that was leaking transmission fluid. I'm also scheduled for work to be done this week to replace the upper engine mount and the transmission toruqe mount.

I've noticed, unfortunately, that infrequently (four times in the last 10 days) there is a "bump" in the rear end of the car that almost feels like the back end has hit a bump in the road that the front end did not hit. If I were sitting in the back, I might be able to isolate the origin better, but I *feel* like it's coming from the driver side rear wheel area. A friend of mine describes it like something is turning fine, then for some reason for just a split second stops, then catches up really quickly causing the "bump."

I have only noticed this at highway speeds (55-75mph) and on smooth roads, though I can't tell if it's happening when I hit bumps on the road b/c I'm hitting a bump... which means what I'm hitting sounds like the symptom I'm describing... I'm sure you see the issue.

One mechanic suggested that I take it out to a dirt road and try to get the AWD to completely engage, and see if that causes a bump. I'm a touch scared to try that b/c if there's something wrong with the AWD, it *seems* like that could make it worse. That same mechanic is thinking it could be a wheel bearing, but again that doesn't sound 100% on-track since the problem is so intermittent, and as I understand it a wheel-bearing will be pretty much continuously annoying in some way.

Anyone have any similar experiences to share, or ideas of how I can troubleshoot the problem? I don't have a garage, or really any tools, I'm just searching for ideas here as much as anything.

Thanks!
--Mike