I just picked up a new i7 27" iMac and hooked it up to a pair of powered monitor speakers. The audio output is very noisy. I get a fairly noticeable humming kind of whiny noise that is even worse whenever I move the mouse. If I hook the monitors up to my FireStudio mobile and use it for audio out, things are dead silent. The problem with this is that I then cannot use the volume keys on the keyboard, which I find very convenient to do. Is your audio out noisy?