Uhh, i guess the on board audio. I just plugged in the headset and started using it.
Then are you plugging into the front panel audio jacks or the ones on the back?
That is probably your problem then. A lot of the time, the cables going to the front of the case aren't shielded very well (or at all) and they can get a lot of cross-talk. Try moving it to the back or to the USB sound card that came with the headset. It should fix your problem.