Some people internally hear music, or various other sounds which may be pleasant for some but to a few, these sounds are quite distressful and uncontrollable. NPR features a story about neurologist Dr. Oliver Sacks and his recent book Musicophilia.
…[his] “book not only contributes to our understanding of the elusive magic of music but also illuminates the strange workings, and misfirings, of the human mind.” Michiko Kakutani, The New York Times