Hello! Today my new pair of Audio-Technica ATH M50x came in the mail, and while testing them I noticed that during relatively quiet parts in music/other sounds there was a slight background hiss. However, there is no hissing during silence. Does this mean I need a DAC? A sound card is out of the question because I have no room in my PC for one. By the way, I currently have my headphones plugged into the audio jack in my mother board. Thanks for the help!