DELL 4320 No sound from internal speakers.....

Hi Took delivery today of this unit - brilliant projector. However I have no sound via devices connected via hdmi........... I have a ps3, wdtv and a pc..........all connect vi hdmi to my tv and all is well - sound and pic. Take hdmi from tv and move it to projector and no sound from projectors internal speakers. VOLUME is up to 20.........mute is off..........hdmi is selected as audion source and speakers are selected as on in the projectors menu.............. What am I doing wrong ? Dave