Using a compressor on the audio track would help remove the huge contrast between the soft and loud sounds, by reducing the dynamic range of the sound.

Check your DVD player's settings too, and if it has a "Dynamic range compression" (DRC) setting, set it to on, this will do the same thing, but it's still best to apply the dynamics to the actual video, because you don't really want to tell everyone to set their DVD players DRC setting every time they watch one of your videos.