i can't hear audio for movie rentals(audio works ok for all other content)

Anybody know how to fix the audio while watching movies on first generation apple tv? On my apple tv, I can hear audio for music, music videos, youtube, internet radio and even movie previews! But..... when I pay for the rental download of a movie there is no audio - just visuals. I am connecting with hdmi. When I connect an apple tv 2nd generation to the same amp and tv, using same hdmi and even same power lead, then there is no problem. ANybody know how I can get audio to work for movies?