Weird "chugging" sound comming from my PC and speakers

[Netherspark]

Ok, when my PC is under load (running wow) there is what I can only describe as a sort of chugging or vibrating sound comming from somewhere inside, and it's also comming through my speakers! If I exit or tab out of Wow it stops immediately.

The best way I can describe it is if someone were dangling a piece of paper into a slow fan -- so at first I though it may be some loose bearings in the CPU fan but I've checked all the fans in my PC and it is definitely NOT any of the fans making this noise. I've even stopped the fans for a moment and the sound continued. It also wouldn't explain why its comming through the speakers too.

I don't believe it's coil whine either. This is low pitch, kind of like a tiny car engine.

What could be causing this?

[Deleted]

Any way you can record the sound for us?