Well, yeah the power supply to the processor xD. It seems like there is an electronic component that has some resonance when the processor is fed with low power supply (when the processor is doing nothing at that moment). Here is a quote from another forum with the same problem:
Welll they returned it within 48 hrs which was impressive. But I can STILL hear the noise! They say they replaced the CPU fan, the heat sink, the system board and keyboard. Not good news. Now what? edit: I just pulled the wireless mouse usb remote off the computer and the sound is gone! must be the mouse! Sure hope so anyway lol. Can't believe it would be so simple. Oh brother. makes sense too because when I moved the mouse wheel the noise changed.
Damnit its still there. But only when it's communicating with the internet updating webpages or downloading data(you know like ALL THE TIME). Better than before when it was a constant noise though. Same sound whether I use wireless or ethernet. This is getting real old.
I tend to think this kind of noise is from the disk drive (mechanical, moving part). Didn't you switch to a SSD? If you have another computer... Unplug your disk drive. Use a USB-SATA adapter. (Assuming you have a SATA drive). Hook it up and mount it as an external drive. Do some file copying to that disk to see if the noise goes where the disk drive goes.
Hi, I am almost sure that the high pitch noise is from the changing of the voltage of the processor. I used the trick posted above and the notebook is really silent when using the windows 7. Also, I switched off the speedstep option of the processor in the bios, and the annoying sound disappeared from my Ubuntu OS too. I hope this helps you.