I think the trouble with this type of sound is its omnidirectional and difficult to pinpoint. I suspect inductive loading between cards/mobo can cause components to squeal. With my previous Seasonic 600 watt it was fine with a pair of 7900 GTO's which would have been <= a 8800 GTX.

Thats the problem with silent systems there's always something thats just a bit louder than something else. Like chasing a rainbow.