no sound on ac3?

[baz-r]

on my dbox2
when go to some channels there is no sound.
if i press the ? key then the green/audio button thay all seem to have english(ac3) selected if i set it just to engish the sound works! brillent
but when i go back to that channel no sound again! until i set it back to englsh(no ac3)
what is the crack then how do i get the ac3 bit to work then? or is there some way of getting the box to pich the right audio?

im sure its simple