I've got this. Keep telling this story often. Pictures in my mind are exceptionally rare. Even dreams are mostly just feelings and emotions or something. But I can "visualize" sound. On couple occasions have even managed to "replay" well known music in my mind near indistinguishable from the real thing (phantom of the opera in case you were wondering). And I got an ability to pinpoint loudest frequencies in a sound spectrum. Think a lot of it has to do with the way we individually interpret the world.