Have your mechanic check the carrier bearing in between the two drive shaft sections. Or, just get under the car and take both sections off the car. Make sure you mark both sections so they go back together the same. Once the driveshaft is out, spin the carrier bearing. If its bad, replace it with a genuine Volvo replacement bearing/mount. It runs about a hundred dollars, plus the cost of pressing it off and the new one on. Also, while the drive shaft is out, make sure the U-joints are free, and not frozen. The U-joints on my car (an 89 740 auto) had little set screws in each U-joint. Take those out, replace them with the little grease fittings, and pump lots of grease in them. Make sure the U-joints are free and not loose. Its hard to tell if a U-joint is frozen when the drive shaft is in the car. Also make sure that the rubber boot is intact, and that the rear splined section slides in and out freely. Read the FAQ as well. You'll understand what I'm referring to when you get it apart. Its easy enough for a do it yourself(er) to take the drive shaft and carrier bearing out in a half hour. While the drive shaft is out, try to wiggle the Piece that goes into the rear end. Also try to wiggle the piece that comes out of the rear of the transmission. Refer to the FAQ if either has side to side play.

bruce