Is there any way (any accessory or mod?) to get the mavic to make different (audible) noises whilst it is flying?

I want to use it as an alarm/alert/message delivery service.

Ive found the ESC on “Find my Drone” but that BEEP is not loud enough and anyway it only seems to work when the done is not flying.  I want to fly a fair distance and get 2 or 3 different (audible) messages to those there who would  listen out for the sounds.  

Interesting idea.

You can try switching to sport mode and jerk it around to make noticeable motor noises.

Sounds like an interesting idea. However, so far, it may not be able to achieve this idea.