faint buzz or whistling sound

[jefla]

I've a 2000 Boxster w/ 45k mi, that's making an intermittent low-pitched monotone hum or buzzing sound that I need to ID.

At first it was very faint, sounding like a bad wheel bearing humming. It would come and go and did not change tone, etc w/ changes in engine/vehicle speed. Now its louder although still faint -- and still sounds like bad wheel bearings I've heard. Porsche mechanic said that's not it, but I'm not convinced he heard it. Anyhow, it sounds like it could be coming from the front or right side of the car, which has me thinking it's a radiator fan. But, it could be coming from the right air vent i.e., engine compartment. I can't get it to happen when the car is parked, of course. (And I'm deaf in my left ear so the **** sound could be coming from anyplace ....). No helpful CEL codes.

Many Thanks