Tuner problem with Denon AVR789 Receiver

I have a new Denon AVR789 Receiver. There currently are 2 hdmi inputs -satellite tv and a dvd deck, and one output to the tv. When I set the receiver to tuner in order to listen to the radio, the sound cuts in and out -it will sound for 2 seconds and then silent for 2 seconds and will alternate like this indefinitely. If I turn the tv set on this "fixes" the problem. I can then turn the tv set off, and the audio will remain correct. The Denon tech support has no ideas. Anyone out there have any? thanx.

I'd rather not send it in if I can help it, as it may take a month before I can get it back.