Dvd audio issues

heres a good one, im trying to make a backup copy of metallica st anger dvd, and since i bought it a few years ago i noticed if its played in my pc, the audio is inconsistant, as in the volume goes up and down. but in the tv dvd p[layer its fine, i used dvd fab platnum express to back up and the same issue on the copy even in a standard player, any ideas? lars seems to be good at choosing encryptions.