Ok, here I go with another lame rookie question. Bear with me.

My '98 C280 has started making a strange low level noise. I first noticed a slight "whistle" effect when I first start the car. Now, I hear it until I get the car moving. At first, I thought the noise was bearings going bad somewhere near the front and I should be able to hear it louder from outside the car. No dice. I can't seem to hear it when I am standing outside the car. Of course, it could be my old ears causing this. With an older American car, I would have thought it was something to do with the heater blower motor? Right now it sounds like a cross between a low level whistle and a squeak. It doesn't get louder when I increase the engine speed. After I put it in gear and start to move, I don't notice it. I believe this is because of the increase in ambient noise. If the car is at idle and I turn the fan motor totally off, I don't seem to hear it. When I bring the fan speed up two increments is where I hear it the most. More speed than that increases the ambient noise level to where I can't seem to hear it.

Is this a common problem with the fan motors?

Thoughts?