PCM stereo is uncompressed, thus higher fidelity than Dolby which is  
fairly heavily compressed. I know no reason why PCM should fall out  
of sync. Have you tried these discs on more than one DVD player, or  
on a computer, and is the problem consistent? Is the sync  
consistently off by the same amount from beginning to end, or does it  
begin in sync and get further out-off-sync as playback continues?

iDVD generates only PCM tracks, not Dolby, and I know of no generic  
problems with sync on IDVD generated discs. So I suspect either the  
discs you're having trouble with were authored improperly, or your  
DVD player has some issues keeping up with the higher bitrate  
generated by PCM (though I have not heard of this being a common  
problem).

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