In my case they rarely have anything to do with the book in question. I read mostly while commuting, so I have my earphones in listening to a general playlist.
Some examples for me:
Powder by Pontypool is associated (completely by chance) to the Powder Mage Trilogy because it was heavily in my rotation at the time.
Space by Biffy Clyro (also serendipitously) reminds me of Culture novels, especially Inversions and Look to Windward.
And finally, the originally released score 'album' for the Bruma part of the Beyond Skyrim mod released in ~2018 reminds me of Oathbringer.
Do you have any appropriate or random associations?
by MyCodesCumpie-ling