I got a concert dvd for xmas. It has audio choices of PCM Stereo and Dolby 5.1. When I choose PCM stereo the audio has this constant loud fluttering static sound in it. You can just barely hear the actual music in the background but it's out of synch with the vocals. It plays fine in 5.1 which is waht I use anyway. Just wondering what exactly is PCM and why do I get this horrible sound when playing it in this mode?