Yes, good question..
I had to think about this for a while. I just can't remember any music at all in my head. I have a running picture in my head of the story and landscape (which is why I sometimes don't like movie versions). My imagination populates the story as I read.
I have found that listening to music while I read, will have an irritating effect when the "action" in the story doesn't match the mood of the music that is playing.