PC makes Hissing noise when running a game.

I'm having this strange noise every time I'm 10 minutes into a game (Stalker COP) and I noticed that when I'm using a VGA analogue cable my display starts to tremble, the noise won't stop until I turn off my pc for 15-20 minutes.
It is constant it varies when a game hangs or if I change my screen resolution, I'm sure it's not my monitor, fans, HDDs, ODD, graphics cards (restarted my pc without them and the noise is still there), I stressed my CPU with prime95 and all went good.
As far as I can tell there's no strange smells, I checked most of my MOBO caps, nothing bad.
Tried a BIOS update, Forceware update...no luck.
My PSU is few days old, My PC runs very well even when there's hissing.

any advise?

It's hard to be sure its not the PSU fan but it's still new why to make that noise? plus, the noise seems to change in loading screens.