Creepy sound when Idle

so, im having trouble with my router, all of a sudden it stops sending IP information so i have to reset it, but thats not the point.

The thing is, recently, i decided to sit in front of my computer and wait for the net to go down again, just staring at the desktop, when i heard a creepy "whoosh" sound, the kind of sound that comes out in those scary movies when the guy looks into an empty room. It didnt sound like a system sound but it definitely came from my speakers.
I wasnt running any programs, and im the only user of the computer so there wouldnt be any extra junk im unaware of. Immediately after the sound i checked the processes, but i found nothing out of the ordinary.
Is there any explanation to this noise? It comes out randomly from time to time, but i always dissmissed it as a system sound. Its starting to worry me now because it came out while the computer was completely idle.

!!!!!!!!!!!!!!11

I was not the only one! Randomly I hear some weird sound from my speakers not very often. But it does happen, and I was also wondering what it was. The computer is completely at idle state, and it is a bit creepy when it happens. Can anyone explain this phenomenon?

mine does that too......................it did it even after i completely wiped my HD and reinstalled windows too........