Hello all and thanks so much for all the tips!

I've had garage experience some 25 years ago and am actually enjoying a more hands on approach to car maintenance with my "new" 96 850 Wagon with approx 155K. Thanks to Mathews and this site, I've fixed my completely separated door stay mounts, ABS module, odometer and flame trap. It certainly helps that the previous owner had around 7k into suspension, t-belts, water pump, tires, PS pump etc ...This car was bought for $1900 and so far I've only got $50 into it including $35 for a "post" purchase inspection by Specialized in Santa Cruz, CA (wonderful folks) that suggested I'm in pretty good shape minus weak coolant and a "little" crankcase pressure--which I'll probably pay them to address (pcv/breather overhaul).

So, no more rambling. This car runs great except once I get up to driving speed, a low level whine presents itself that is NOT tied to RPM. It does seem to shift between 2 or maybe 3 frequencies. The sound goes away when I slow to an idle--which is making it hard to locate. It also doesn't seem to manifest itself when parked at higher and held RPM's. There is no performance problems, but being that I work in the sound field, noises like this drive me mad. Funnily, the day I had the car inspection, the sound was not obvious.

Air pump? some valve - vacuum leak ?

Thanks for any insight here...

 

Without hearing it would be impossible to say; first thing that popped into my head was that transmission whine you get when the torque convertor starts to go bad (knock on wood...).

You could either get a recording of it, post it on utube, then post link here, or take it to your trusted shop and see what they think.

 

Would the torque converter NOT follow acceleration frequencies ? It's a very steady pitch, but it does "shift" to different notes at times hmmmm...

I'll do more hearing tests and return. Thanks

 

I didn't say it was torque convertor; just said that's the first thing that popped into my head. From your description we can probably rule that out.

Again we would have to be able to hear it to go any further; as you have found it's very difficult to describe a sound...

 

Well, this would be a nearly impossible sound to record given how it blends in with other ambient noises. I do pro field recording and could give it a shot, but it would take some doing! It's so odd somehow that it fades away when the car isn't moving. While driving, I can go into neutral and the sound stays audible. It really sounds like the air pump going off at the wrong times, but I really I haven't a clue here. It couldn't be the fan?? Symptoms are the same as described and given how subtle it is, I think I'll just try to forget about it for awhile.

-Ed