Volvo Repair: Vibration When Turning, differential unit, volvo dealer

Question
About 5 weeks ago I purchased a 1998 V70 AWD wagon with
85000mi. Since I took delivery of the car it had a vibration
mostly when turning left and slightly when turning right. It
would start when the steering wheel would be turned 1 or 2
turns and continue vibrating until you started going straight and
then for another 10 to 20 sec. while going straight. The
vibration is strong enough to shake the steering wheel and
happens under 20mph. It went back to the Volvo dealer whom
has spent 2 weeks on it and told me yesterday "we have
exhausted all of our options to repair it". I know they replaced
axel shafts and u-joints plus other things they did not tell me
about. The said they are calling Volvo NA to get a Master Tech. like
yourself to look at it next week. The car was serviced at
this dealer since new and is fully documented for all of the
repairs. Any ideas?  

Answer
without seeing it it is hard to say what may be wrong.I have seen some problems cause vibrations from the rear differential unit.I am not sure if it would shake the steering I believe it was felt more in the body.on some cars of this type there was a bulletin for installing a dampener on one of the axle shafts ,but do not recal the exact specifics of this.

they will be getting a field technical specialist who works for volvo corporate.to look at it.