The state of the diegesis of sound within film is, for the most part, pretty much straight forward leaving little, to no, discrepancies between diegetic and non-diegetic sound. Nevertheless, occasionally directors will play with the diegesis of sound within a film. The is most commonly employed and effective in comedy films, wherein this playing with the diegesis adds to the humor of the film.
A prime example of this is occurs in Tom Brady's, "The Hot Chick". When Jessica and her friends go into the voodoo store to check it out, once she picks up the magical earring box a loud, drowning ominous throbbing drum bass comes in. This is a fairly well known meme for most people because the understand that sound is used, in this case, as a means of influencing the audiences understanding and emotional reception of the subject matter. Usually, the viewer understands that this sound is non-diegetic and is just employed as a cinematique tool. However, in this scene, while one might believe that the sound is non-diegetic at first, we come to find out that it is infact coming from a Bongo playing character in the store, played by Adam Sandler.
Another instance in which the diegesis of sound in film is played with for comedic purposes occurs in the film "Theres Something about Mary". Throughout the course of this film, the majority of the music is played by a musical duo who are situated outside of the scenes, yet inside of the world of the film, usually up in trees playing there instruments.
This is the link to the clip in "The Hot Chick", referred to above:
http://www.youtube.com/watch?v=iiGki-_iD3I
