Tonic Please,
I've played around with all the settings. I have uninstalled and reinstalled NvDVD and played with S/PDIF settings, interlacing settings and other sound settings. I do suspect that it has something to do with my WinTV card and software. I often record off the WinTV card and then play back in WMP. I wonder if this is causing confusion with the interlacing settings.
Anyway, it is still a problem. I will try Scallywag's suggestion and see if that works.
Thanks very much for you continued help on this. If you are ever in the Tempsford area I'll buy you a pint or two.
DeepC