I plugged in my TV and was suprised to hear a distinctly audible "Hum" coming from the back of the TV. After letting it run for awhile the Hum diminished,but never fully disappeared. Anyone else experience this? Faulty set perhaps? I pressed mute and that had no effect on the "hum" so it's not a sound/speaker/interference problem. The Hum changes pitch as the video image changes. Lighter background images appear to produce the loudest hum.