You might want to search the archives. When the XC70 was first introduced in 1997/1998 there were a lot of problems with driveshafts balance and vibration. I think Volvo even had different weights of bolts available to correct the problems. I don't have an XC, so no direct experience, just my often faulty memory.

-BTC

'98 V70 T5 5-speed, 166k mi, front IPD stabilizer bar, rear factory HD bar, Bilstein HD, Volvo strut tower brace and skidplate, e-codes, V-1, Mobil-1 since new

"A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools." -- Douglas Noel Adams (1952-2001)