ok it does work but not as it should....
I've worked out that when I save the audio muted... It does not mute, however, if i fade out the layer in which it is playing, then fade it back in... at this stage it is muted.
Restart the video again, and it un-mutes.
A work around is that i've added a fade audio and video effect of 0.1 seconds to the video and its working as it should now.