Hello Rich,
Some of those pieces of music are deliberately louder to accentuate certain points in the games narration. Like the Mad Mage’s Mansion, Gates of Ravenloft and of course the Bravery in Barovia “heroes theme” that kicks in on the Old Svalich road. These, I see are opportunities to absorb the surroundings in sound with the text from the book. After it has played, there is the more subdued sounds of the area your heroes are in.
This is my effort to try and get a film like feel into your game.
Can I ask if this happens every time you click on this mood, that the music is really loud? I ask as I know that there was a bug that would come up every now and then. Playing a random element and 100% volume. After clicking on the mood a second time it would then reset to correct volume.