Hum in the audio - 32'' Proscan 1080i

Question

There's a very distracting hum/noise when any audio plays from the tv. The hum goes away when muting, and when the volume is at zero. The hum at level one on the audio graphic display is the same noise at any other level. My cable box does not have the ability to adjust volume, so it shouldn't be getting too much signal. Any ideas?