Researchers have figured out how make shaped drone rotors that convert audible and ultrasound frequencies into stable mechanical spinning motion, leading to tiny drones that can be completely silent. While scary-sounding (no pun intended) it’s unclear how usable these would be in the real world, since a line-of-sight source of sound waves has to be provided.
You claim that your kite operates without making any noise, and yet it is powered by wind, which is quite noisy.
Kites are noisy.
flap flap flap…
Humming string etc.