I've got a lovely 27" iMac i5 connected via DVI>HDMI to my LG HDTV. When I have the TV on to watch regular programming via antenna, my Imac goes crazy and starts refreshing and flickering the screen. I have to put the Mac to sleep to be able to watch anything on the TV other than a pure DVI-out feed from the iMac. Any thoughts/suggestions? It's annoying that I have to turn off the Mac everytime I want to watch TV, and I don't want to have to go unplugging cables to do the same either.