Strange iBook G4 noise

So I was using my laptop tonight, when I had my head near it, and I heard this slight noise. It almost sounded like a super-quiet sizzling noise, like a very small fly trying to fly. I know its not from the DC-in board, because the laptop charges fine (sometimes the DC in board makes a buzzing noise if it is not working properly, mine is thank goodness), it seems to come from the left-hand side of the laptop. Its not like a hard drive clicking, I've ruled out the HD. The noise is coming from farther up. Is it part of the MB? Processor maybe? When your in a quiet room by yourself, you can hear it barely from an average distance away (maybe a foot or two). Anyway, its kind of annoying. What is it? Is it normal?

EDIT: I have another iBook MB, and I turned it on, but I don't hear the same noise at all, but that doesn't really mean anything.

OK it comes from right on top of the processor, but I don't hear it this morning... What exactly are power ICs?

OK, I was just concerned because I hadn't heard it before, and this iBook is relatively new to me.

I hear it now whenever I have my head close to the computer, and now I'm not sure if it's the graphics card or the processor. Whenever I am scrolling or something like that, it seems to make more faint noise then when idle. Bizarre.

Ok, it just makes me kinda nervous, I've read that sometimes it means a bad GPU or CPU, and then I would just have to replace the entire iBook, as you can't just put in a new processor!