Hi,
I've got a '94 850 sedan - 136,402 miles to be exact. Recent repairs: gear switch (got stuck in "winter mode"). Yesterday drove it an hour on the highway, was travelling at 75mph, noticed a very loud high-pitched squeeling noise that seemed to be coming from the center console. Thought it was the radio, turned it off, turned it back on, tried the vents, nothing affected the noise. The noise stopped about 15 minutes before I reached my destination, and didn't reappear when I was starting the car to leave or on the trip home. Only thing I've noticed is when starting the car up (in the last week) the aux. belt is sort of chirping - the car is due for a timing belt/aux. belt replacement in another 2000 miles. Any advice greatly appreciated. (As in, should the car be serviced immediately before any long distance drives).
Thanks.

Have you considered it might be the AC/Heater fan? Mine "squeals" but it is very temperature sensitive.

Sounds like a/c compressor locking up,alternator bearings failing,or belt tensioner bearing failed.
Of the three,tensioner is most likely.
HTH.Jeff.
--
whilst

Jeff,
Thank you for your response. Does the "chirping" sound that the aux. belt is making indicate to you a failed belt tensioner bearing, and this is what could have produced the transient high pitched deafening squeal? And in your opinion, should I simply get the timing & aux. belts replaced now, along with the belt tensioner (replace the whole belt tensionser?) instead of waiting another 2K miles? Because presumably if I wait one of the belts may suddenly fail, which would undoubtedly not be a safe situation -- I assume the belt tensioner is critical here?
Thank you very much.

Not only unsafe, very costly. The timing belt failure while the engine is running is catastrophic to the engine.

Thanks you guys for the help. Funny, the service manager at my dealership didn't think it was unsafe to drive this way. I'm also wondering why the belts would be crapping out now when technically they had another 2K miles of life to them. My Volvo has gone across the country twice, and I only started getting problems with it when I got back to the east coast: driver's side door stop replacement and body weld, left front ball joint replaced, front brake rotors resurfaced (big mistake - should have had 'em replaced) and factory brake pads put on, gear switch replaced, front windshield replaced, and now this...We're talking over $3K here.