Supress USB Soundcard Hum

[SYNACK]

With our Multipoint systems we use up to six directly connected monitors and usb hubs each with a mouse, keyboard and soundcard. For the most part this works great with Multipoint Server 2011 (2012 is junk) but we get obvious hum from the soundcards. Does anyone know of a cheap way to remove what may be ground loop hum form a soundcard output?