finnishcolumbia

I am not a computer audio expert. But I have been using a USB DAC for a couple of years and have been very happy with the sound. Recently I moved my computer to a closet in the basement so I would not hear the fan. Now get a hum when I play music. I get it using winamp, windows media player, or pandora. The hum does not change if I adjust the volume. When I shut down the application, the hum disappears. Any ideas? Is there a better way to make a long USB connection? it's about 25 feet