I wrote a few weeks ago stating that after a serpentine belt change, the car had a bad vibration, which was worse when the a/c compressor was on. The Volvo dealer had me change out the lower sub frame motor mounts, and this did not solve the problem. We looked for a heat shield that might have gotton bent and was touching, no luck there. They could not figure it out. I kept looking and last weekend was under the car and noticed that an a/c compressor mounting bolt was backed out about an inch. I put my auto stethoscope on the bolt and got the asnd noise noise I had been hearing. I took it back to dealer to screw in the bolt because I couldn't access it. They ended up finding several loose monting bolts, had to remove the compressor, alternator and power steering pump to get access to the mounting bracket and retap the threads in the bracket, but once all that was tightened, the vibration is gone. Cost $320 to screw in a bolt.