When idling I hear whining noise

1999, 3.1 L lumina. I hear like a whining noise when the car is idling. The noise goes away when I increase the engine rpms. Sounds like it is coming from behind the steering wheel. It is not a loud noise, but it is there. It is not the inside fan or the serpentine belt, I already tried those. Could the brake master cylinder make that kind of noise? It feels that it comes from that area. The noise comes and goes. Any ideas?

Thanks!

I don't think it'd be the MC, if anything it'd be the booster. But I imagine it could be the rack, the PS hoses connect there I think. Though I'd imagine you'd hear the Power Steering pump make noise before the rack if its just at idle.

Try to pinpoint it using a long handled screwdriver or a broomstick put to your ear. Listen for where the noise is loudest.