This weekend I watched the 2013 Alexander Payne film, Nebraska. In it, you can observe both diegetic and non-diegetic music. Toward the beginning, David is attempting to sell stereo equipment. They show him in a room testing the sound equipment for customers. The music you hear is diegetic because the characters on screen can also hear it. The background music accompanying the majority of the rest of the film would be considered non-diegetic. What movies did you watch?