Vibration from rear of vehicle...only in reverse at idle

[drmonkey]

So the last week or so I've been getting this weird vibration at the rear of the car when I'm in reverse and at idle (doesn't do it when moving in reverse). It doesn't do it when I'm in drive though...or at least it doesn't feel as pronounced. It's strong enough to vibrate things in the cabin. I just rolled over 100k. Could anyone help point me in a direction? I'm thinking maybe the diff mount or axles? I'll be putting the car up on jack stands this weekend but it would be helpful to know where to start looking.

Thanks for any help...

[mtroxel]

Take a good look at the drive shaft back there too. Those can make funny vibrations. There should be 0 play in the CV joints at the ends. Put a flashlight behind the rubber on the center bearing. I almost missed it on my B5 shaft. Rubber didn't look too bad on the car. Put a flashlight behind it and I could see it coming through a crack. Get it off the car and bend it a little and this is what I saw.

[drmonkey]

Take a good look at the drive shaft back there too. Those can make funny vibrations. There should be 0 play in the CV joints at the ends. Put a flashlight behind the rubber on the center bearing. I almost missed it on my B5 shaft. Rubber didn't look too bad on the car. Put a flashlight behind it and I could see it coming through a crack. Get it off the car and bend it a little and this is what I saw.

I was hoping someone wouldn't say that......I'll check it out. Last time I had it up I checked it and the bolts at the driveshaft flanges since when I bought the car 3 of the bolts were missing from the transmission end. I torqued them all to spec and checked them 6 months later (on both flanges).

Appreciate the tip, I'll start there.

[mtroxel]

Ya never know till you look, but it seems more guys have problems with that drive shaft than they do with the pumpkin or the rear half shafts.

Same shaft/center bearing when no one's pulling on it. Doesn't look that bad.....