Apparently it can also happen on new digital tvs, as the signals are processed after receipt and OS glitches can cause the sound to get out of sync. In that case a channel change or a 'reboot' often fixes it.
If you report the issue to SBS with your location they might be able to fix it. Tell them it is an analogue TV (unless you are using a digital set top box in which case it is the same as the problem above). I think they will still be airing analogue for a few months yet depending on location.
