16 mm film   

Film format for low budget, documentary, etc. film. Runs at 24 fps which = 7.2 inches/sec (40 frames/foot).  This relatively slow speed, combined with the use of a low bandwidth optical format for its mono audio make 16 mm films notorious for low fidelity soundtracks.  To exacerbate the situation, one rarely finds a 16 mm projector with the optical system properly aligned.
Some additional reasons for 16 mm's poor audio:
(1) sprockets stick on the transport mechanisms causing wow & flutter.
(2) because the image needs to be stable during projection, the film actually stops for each frame.  Although the loop between the projector gate and sound head is meant to buffer this disruption, some distortion inevitably occurs.
(3) dirt or scratches to the film alter the sound.
(4) film stock (black and white/colour, various grains, etc.) will affect the sound.  For example, high density colour sounds better than black and white stock.