Volvo Repair: 98 V-70 AWD drive line vibration, rear axle shafts, rear drive shaft

Question
Thanks.  Only vibration is when moving and only at those speeds though as it gets worse it expands more. Seems if the problem were the rear drive shaft (connects rear differential to trans) that something would have been different when it was changed or balanced.  Therefore I think it may be in front or rear axle shafts or CV joints.  Could one of them be dry and binding or out of balance?  Or could it be a front or rear motor mount that is soft or collapsed so that under just the right combination of speed, motor angle and so forth that this hard but small vibration sets up?
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Followup To
Question -
My 98 V-70 AWD with 166,000 has been developing a dull vibration (like a frozen U-joint in an ordinary rear wheel drive car) during the last 30,000 miles and recently gotten much worse. Ocurrs at 32-35mph and 63-68, at times more pronounced than others.  During this time I have run three different sets of tires, always same vibration. The drive shaft was replaced with a used one (bad center bearing) but no change in vibration.  Volvo mechanic replaced "drive shaft balance bolt", no change.  A different Volvo mechanic at another shop replaced the right motor mount - no change.  He thought it was not the bevel gear because there was little noise. There is no clicking in CV joints.  There is however a swishing or sloshing noise when the car is in gear at idle, but transmission works perfectly, always has, no repairs ever to engine, transmission or driveline except above.  Original suspension parts, struts and self-leveling shocks.
Stumped!
Answer -
Well the only thing I could think left is the main engine mounts.  The right side one is for balance only.  I have had several XC90's and XC70's where the car runs great but has this vibration that you can't seem to pinpoint.  It has usually been the front and rear engine mounts.  Kinda of a pain to change, even with a lift because of the subframe design on this car.  Usually you can feel it at idle with this problem though.  Is your problem only when driving?  It could also be the driveshaft itself.  I have had several go out of balance and it is ALWASYS the hardest type of vibration to locate because there is almost no way of telling it is the right or left side.  If it is an axle though it will feel fine at idle or coasting but will start vibrating again once you get into the gas.  Hope that helps.

James

Answer
Well one of the CV axles very well could be out of balance but there is almost no way of telling which one is causing it.  Unlike a wheel bearing the vibration won't change based on the movement of the vehicle.  Those axles aren't cheap either so it is very hard to spend that kind of money on a guess.  If the motor mount failed you would feel the vibration based on engine speed, not vehicle speed so check it when the car is still.  Your CV axle is probably the most likely culprit but have a GOOD mechanic look at it to determine which one may be causing it, and see if the shop will cover the repair if they misdiagnose the problem.  Some shops will cover a second repair attempt if they performed an unneccesary repair.

James