I've been experiencing the same weird noises on my 20" Intel iMac. What's scary is that I hear a faint noises when the iMac is off. 😱 The sound does not stop unless I unplug the AC cord. 😕
My iMac intel makes the exact same whine. Fortunately, I don't turn the computer off very often. Do you think that it's something that can be fixed with a firmware upgrade or something I should talk to Apple Care about?