High-pitched but constant whine while moving

[Larmor]

For a while, I've had an occasional high-pitched whine from somewhere up front in my '93 850 while moving -- never happens when I'm stopped, and it's hard to tell exactly where a sound that high is coming from. (I think it's engine compartment rather than front wheels, but can't be entirely sure.) It used to happen only in cold, wet weather, but lately it's been popping up sometimes even on dry summer days... not every time I get in the car, maybe twice a week tops.

What makes it odd, though, is that the pitch is almost constant -- it's got some wobble, but doesn't go up or down according to braking, engine speed at all, or road speed above about 20 MPH. Decelerating below that, it'll quickly go up even higher in pitch until about 15 MPH, below which the sound disappears. Usually it goes away after about 10-15 minutes of driving when it happens. About 3 times out of 5, it begins a minute or two after a cold start; the rest are at apparently random intervals in mid-trip on a hot engine.

Brake pads look fine, no signs of uneven wear or rotor warpage, and I'd think that a rub there would depend more on road speed anyhow. My first thought was the serpentine belt, but replacing that hasn't done anything. My second thought is the serp belt tensioner, still the original. Anything else I should look at before ordering more parts and hoping for the best?

[phils94850]

have you checked the wheel bearing ?

[Ozark Lee]

Do you have SAS? The SAS air pump will squeal like a banshee as it fails and it is not speed dependent.

...Lee