The sound heard from the UH1 (Huey) helicopter is the sound of a 3 bladed helicopter (like the SA341G) A Huey helicopter makes a more "flup-flup" type sound instead of the "flutter" type sound heard.
When the hijacked police helicopter is descending over a desert area, an area of with houses can be seen for a few frames. Possibly taken from stock footage of another episode or the movie.