Strange Whirring noise

My computer has a strange whirring/whining noise. It is not normal coil whine as the pitch does not change relevant to what I am doing and it still continues even though v-sync is on. I have checked all fans manually (by spinning them down carefully) and its not any of them. I tried the toilet roll tube to the ear technique to no avail.

When the computer starts it is completely gone, no whining at all. Even when playing games for a while it is still not noticeable. after a while it starts in the loading screens and when the game loads it goes again. Eventually it happens constantly getting louder until it levels and is audible even with headphones on.

I had a problem with coil whine on my graphics card however I solved it by enabling v-sync all the time through the catalyst control panel.

I have absolutely no idea whats causing it.