Volvo Repair: 1998 V70XC low speed vibration, driveshaft repair, v70 xc

Question
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Followup To
Question -
I have a 1998 V70 XC with 60,000 miles. No accidents. It has a vibration that shakes the car between 13 and 18 MPH.    It occurs when going straight but is worse when turning in either direction. It is not apparent at higher speeds even hard turning around corners.  The car can be in gear or neutral (coasting down from say 30 MPH, the shaking starts at about 18 MPH and stops at about 13 MPH.  It is nothing obvious. Tires are round and balanced (wheels off car), and alignment was done. A mechanic had it for 3 days and couldn't figure it out.  At work I have similar experiences with centrifuges that vibrate when passing through a specific speed either going up or slowing down. Thanks for your input.
Answer -
it could be one of the front drive axles.I have seen the drivers side one cause a vibration similar to this.there was a bulletin for installing a dampener.I will try to find it.

If it is one of the drive axles, can they be examined for trueness or is it a "replace and hope" process.

Answer
I am not sure.I have never had one checked.I was still trying to find that bulletin. it was an old bulletin though before our computers.the only one I have seen give a problem is the drivers one.I will still look for that bulletin. I would try asking a local driveshaft repair shop if they can check them they might know if it is possibl.