sigh. My recent problem. On games that give me coil whine (200fps +) I can hear it coming from the headphones as well. Shit sucks.
I had that on one of my previous soundcards, a Xonar STX.
It picked up noise from the line in, which i didn't use anyway.
So i just muted that in the windows recording devices tab and all coilwhine in my audio went away.