So, I am probably not alone in noticing that any processor makes a high pitch buzzing sound while working, and this sound is more noticeable and varied in pitch when computations are performed. I also hear it from the GPU when doing operations like dragging a window around.
It's not the fan. I also recall a group of hackers at some badass convention recording this noise while gnupg created a key, and got some information about it.
Here it is: Acoustic cryptanalysis
What physical phenomenon produces this sound?
Here are some other reports