I'll listen to music if the book mentions it, but otherwise would find it distracting. Can't imagine throwing on random classical music that may not even match the period, it'd be like having two different emotional tones going on at once.

My dad described Bach's St. John's Passion as 'nice, Churchy music'. I tried to listen to it, it's just full of a sense of religious awe/terror, despite being a militant atheist, ended up an emotional wreck. Not all music is that emotional to potentially clash with a book (or not, maybe) as much, but a piece like that, I can't understand how it could even not bother someone.

I am also into opera so the line between books and music as narrative doesn't really exist as much, maybe. There's quite a lot of opera adaptations of books/plays, too! (Sometimes the opera version has become the more known, like Carmen, La Bohème, though those two also made a lot of changes to the source material)