I have a 94 850 that would make a groaning noise at slow speeds and would sound like the brake dicks were warped. It turns out that the wheel bearing was worn badly and the noise came from the bearings because the seal was broken letting in water and dirt. I replaced the bearing and no more noise. I'm going to do the other side next because when I make a left hand turn, the brake disk rubs the pads.
I hope this solve your problem.RK

I was told by one pro mechanic that when replacing pads on a volvo you do best at avoiding noise by using factory pads and making sure all the shims behind them are in place and greased.

That said and done by me I have got brake noises, mostly squeal, time to time, not correlated with anything except possibly cool wet weather.

also just an FYI if you go with the hard ceramic pads and cross-drilled rotors, you'll get whistling most time you lightly brake. The car will stop quick when you need it to but when you ease to a stop its loud.. The 60-0 fix works for a couple of days then its back to squealing... If you have the Volvo pads, it should fix itself with the 60-0 stop because they're softer.. Just brake hard a couple of times a week and it shouldn't reappear..

Before you go through all of that expense, you obviously don't DIY, find an empty road and do a couple of hard 60-0 stops. 2500 miles/yr on new pads could leave a lot of gunk on the pads and rotors, and bedding them in once in a while is better than new pads.

Klaus