'Humming' from LG TV...but speakers DO work!?

I'm at my inlaws house, they have a 1yr old LG LCD TV model #47LH85 w/ a wireless media box model #ASW1000. The TV and media box both seem to be working fine. However, there is a humming noise coming from the TV speakers when any input OTHER than TV is selected. When the TV input is selected the speakers work fine, select anything other than TV and a loud humming comes from the speakers. I have even unplugged the AV cables from the back that run to the dvd player [the only other component we are using] and when selecting any other input from the media box the humming comes from the speakers.


Again, the TV speakers are fine, and work, but only when TV is selected. The cables are also not the issue, b/c the hum happens even w/o them plugged in.


Thanks for your help.