Had a thought this morning on my drive into work that may be a game changer or a totally stupid idea. So, I was a teenager in the 90s. Back then there was a new product called the Cyclone made by Phoenix Gold. Basically a DC motor with a plank on it that vibratted to make sound. This is an old idea as many kids, including me, found out that when you put a toy motor to a sound source you get ... sound.
Then I connected the dots...
So, when an RC motor gets plugged in there are all sorts of beeps that can be played. Basically by sine wave generation... Can a simple sound source be sent to the electric motor while the prop is spinning? Now, I assume this would take away some power from flight but most electric setups are overpowered anyway. Its something I may play with this evening. Not sure if the signal can be sent through the signal wire for the ESC or if you can just use the power leads for the ESC.
Like I said, either a good idea or a bad one.