tryagainslam

Hi, i bought an HD500x a month ago, and it was working fine, i record my guitar with cubase and it sounded ok, without noise. Today, i started recording with the USB and I heard a noise that only appears when i play something on the computer (While the HD500x is connected to the pc and using my headphones) or when i am recording through the USB. Besides that it works ok, but i would like to eliminate that noise.... does someone knows what to do?