Powerbook strange noise problem

Hey, I know that "strange noises" eminating from powerbooks have been discussed before, but I was wondering if anyone has had a problem like this:

When I put my cursor over the dock and the icons expand, I hear a VERY quiet long clicking noise. It sounds like you are dragging something over a surface with ridges. Its not coming from the speakers (so far as I can tell) because I have external speakers plugged in, yet the sound comes from the powerbook. It sounds like it is coming from the upper left part of the case.
This may have been a result of upgrading to 10.3.5, as I don't know if it made the sound when I had 10.3.4. Any suggestions?