Hi,
First I thank everyone who contributes to these threads as they are really helpful. We have a 2011 XC70 with 90,000 miles. It has developed a transient vibration at roughly 25-35 MPH only when accelerating. It happens regardless of what gear it is in and can be felt in second, third and fourth gear. Currently it does not occur at higher or lower speeds. The vibration is clearly coming from the rear of the car and can be felt most in the floor (according to my kids who sit in the back and were drafted into diagnosis roles this afternoon). I have had it to dealer once and they needed more time to evaluate, which will happen later this week. However, they mentioned that it could be rear differential, and this sounds quite expensive and I can't find anyone saying these have big problems on this car. I am hoping to have an idea of what might be wrong before going in so I can try to decide whether it will be worth it to fix it. The car has been very reliable with only a couple thousand of maintenance that bugged me (trailing arm bushings and the aux. drive pulley (very expensive to replace--$1500)). I was hoping to at least get another 5 years out of it, but I know how Volvos can get expensive to repair as they get older. Thanks very much.

 

Update:
It was determined that the AWD system is problem as disconnecting rear portion eliminated the vibration. The AWD pump is not the problem, which I am told leaves the AOC clutch. Any ideas of how to change this for say half the money the dealer wants to charge? Thanks.

 

As a last effort I took the car to another mechanic and the propeller drive shaft joint was bad. It was replaced and the vibration was gone. Dealer was way off the mark.

 

Glad you figured it out!