Do you have any USB devices hooked up to the front panel as well? I have the same problem with my case (Antec TX-1050B) when I have my Logitech G15 backlit keyboard hooked up to the front panel. I think its a problem with the signal wires for the audio and USB not being well shielded from each other. Whenever a device sends data and/or power through the USB bus I get noise (which is all the time if I have the backlighting turned on). My solution was to hook up the keyboard to the back of the motherboard rather than use the front panel.