Audio from DVD player volume changing!

[god_is_american]

I dunno if anyone can help me, but when I play DVDs in DVD player the volume moves up and down seemingly random. I use optical out to 5.1 surround system as well as the regular speaker output to an amp and speakers (for music). The volume changes affect both outputs. I do not get variations in volume when using iTunes or when playing a DVD through VLC.

Any ideas?