A common, though not universal, problem on the S80 as well.
You did not specify if the noise is in the drive train or from chatter as the blades sweep across the glass. The latter problem is common on S80s (I had it during the first month of ownership) and appears to be caused by the Volvo windshield washer fluid, which damages the wiper blades. To eliminate this problem, buy new aftermarket wipers and blades (I used Trico, about $15 for each side), and flush out all of the Volvo washer fluid. Replace the fluid with any other brand. Clean the glass with a cleaner specially formulated for automotive exterior windows (not Windex). I use Clearvue, made by Turtle Wax.

If you bring the car to a dealer for service, be sure to emphasize that they under no circumstances are to add any washer fluid. Even a small amount seems to contaminate the rest, and the noise will return. I always ensure the reservior is completely full before service, so there is no room for them to add more.