I'm not exactly sure what your problem is, but on my 1998 V70XC
(basically the same model) the brakes have been emmiting more of a
low-pitched "hum"-ish noise for about the last 80,000 miles...pretty
much forever. After talking to my mechainic a few times and the dealer
at a free diagonostic clinic, I have found a striking conclusion:

With Volvo's commitment to safety, they are using bigger and bigger
braking systems, especially on the super-safe V70s. However, a normal
driver does not need anything close to that sort of power in day-to-day
driving. With these modern braking systems, a sort of cleaning system
is built in to eliminate road dirt, which can cause squeals and squeaks
unneccessarily. However, for that cleaning system to work the brakes
must heat up to burn off that road dirt -- and for such heating to
occur, they have to be applied near maximum power. It's kind of dumb,
isn't it?

So the only way I've found to clear my squeaks and clean my brakes is
once a month, I take it to a large open parking lot, accelerate as
rapidly as I can, and then slam on the brakes all the way. It must look
kind of funny from outside the car, but it works.

you must use volvo parts especially when it comes brake pads