When I shift into reverse or any forward gear, my truck will periodically make this whining noise. It has only happened when I am not moving. Not sure if it has to do with motion or just the lower RPM. I put it in park and it stops, neutral it stops... reverse or any forward gear and it is like the fan belt is making that noise or power steering pump or something. It is a whine, not very loud but loud enough to hear over my exhaust with the window down only. I had originally thought this was my power steering pump but I wasn't even moving the wheel back and forth this time when it did it. Any clue? I could just replace the fan belt but I wanted to see if anybody knew, and the fact that it does it only in gear is strange to me.