Don't know what the official name for it is ... motor noise ... alternator whine? Anyway, I got it. I just bought the car (92 convertible) and stereo is factory. I don't hear it all the time, and suspect it is only coming from the rear speakers or rear right speakers. Also, whenever I roll the windows up or down I hear it too (from all the speakers I think, when operating windows). It is a low-mileage car, so I don't think anything is worn out. I assume it is a common problem out of the factory.

Any suggestions on what to try first?

Thanks!
Brian