Turn your computer and monitor off. Now just use your guitar and cable that you have been using when there wasnt any noise into the Hd Pro and listen with the same headphones/speakers you used before with no noise. Do you still hear the new noise? If you do, replace the speakers with headphones (or another speaker/amp) and if u have access to another guitar and cord use them now. Do you still hear the same noise? If so, its coming from the HD Pro.  Repair time Im afraid at this point.