This has been thought of before. But they were shut down pretty quickly because it's illegal to rent out music recordings. Besides people would just be ripping everything to their harddrives anyway. The reason rentals work so well for movies and not music is because people use them differently. Movies are most often watched once and music is listened to over and over again. So it's much more economical to own music (because it's used over and over) than it is to own a movie which typically only gets used once.