I haven't been watching Come Dancing, but do get occasional sound drop-outs for a second or two on various channels.
The drop-outs seem to happen on any channel, not only HD.
I have Sky+ HD and connect to TV via HDMI (as you would expect).
If I use live pause to rewind and play, the sound has been recorded.
Also, the sound is not interrupted on the RF out connection - How do I know - Listen to both TVs at the same time - you can hear the second one when the primary goes silent.
As this seems to be common, is it really acceptable. I think it's just a processing issue and could potentially be worse depending on the channel and protocol ude. Difficult to recreat and therefore recognise and fix the root cause. Sky don't seem to be interesed, but it can be annoying (I missed Thierry Henry say he handled the ball).