Odd high-pitched noise?

[jknight8907]

My 13" Macbook Pro has started making an odd, high-pitched noise, kinda like one of those 'mosquito' ringtones. It's pretty quiet so I can only hear it at night when the computer is beside my bed on the nightstand. However it's odd in that, it's always present UNLESS I scroll in Firefox. As long as I'm scrolling in Firefox, the sound stops. Crazy. It seems to be coming from the left side of the computer. Any ideas? Thanks

 

[Benjic]

If the noise goes away when you scroll, it's your CPU idling, it's a known issue with Intel CPU's. Best thing to do is to get used to it.

 

[Lucbert]

As far as I know all Intel Core 2 Duo Processors have this "problem".
If it really bothers you, you can try to but some load on your CPU in order to get it out of idling state.
This can for example be archived by starting photobooth.
But keep in mind that having load on you CPU will reduce battery life.