I have a 2002 V70.
I got a pearcing squeel a few weeks ago.
I thought it must be the belt, so I replaced it.
Seemed to slack off when I did. But soon enough it got worse.
I thought maybe it's a bad pully so I pulled the belt and checked the pully.
They seemed to be fine. I had about enough and wife was pegging out the frustration meter so she took it to a mechanic this morning. Before popping the hood he said you have a bad oil trap. We've been to this guy before and he's one of the most honest mechanics you'll find, so I trust him.
he pulled the dipstick and the squeel stopped. put it back and it started back up.
I should also note the car has been running ragged here lately also, supttering, rough idle even stalling.
Does this sound on line that it is the Oil Trap?
I have found a few posts on how to replace it and I am on the fence with doing it myself. He estamated $400 to fix it. Sound fair?
He's also changing hoses and gaskets along the way.
I also found somewhere that mentioned a Fire Trap. Should it be changed as well?
Is it the same thing?
Any help or advice would be greatly appreciated

I have a 2001 V70 with 115,000 miles and had the same thing. Same rough idle and stalling and squealing (like you I thought it was a belt). Dealer replace the Oil Trap for a little over $400. Has been fine now for about a year. I did have
a new Oil leak right after the dealer replace the Oil trap, took it back to the dealer which indicated it was not related to the Oil Trap he just replaced, indicated it was the main oil seal???? I did nothing and it has not leaked since. Not sure if they caused something temporary or what, but again it's not leaking anymore. Hope this help.

Yeh there is a diaphragm in them that breaks with age and causes the noise, that's a decent price to get it replaced.