I've been having this noise for the last three days from my Macbook Pro. It does not seem directly related to the fans; it does snow an increase when fan speeds are higher, but you can hear the fans themselves so I think it may be something different. I'm stuck using this computer while volunteering in a rural medical clinic in Turkey. I have applecare and I already contacted firstname.lastname@example.org last friday and nobody has even sent me a reply. I think I'm on my own!