I noticed this the other night when watching spider man 3 from anytime.
I had put this in the planner and had watched the first hour the night before with no issue.
So sat down to watch and the audio was terrible, dropping out all the time.
I was recording the movie Greece in hd at the time.
Stopped it playing, back the live programme and started it again, still dropping out.
I waited 20 minutes until it had finished recording and played it and the audio was perfect.
So for some reason my skyhd box was having difficulties with the audio on an hd movie when recording an hd movie at the same time.