[1] https://theconversation.com/drones-to-deliver-incessant-buzz...
That's absolutely ridiculous. The quiet ones might be that low, but others can go well over 100dB.
(which is not intended to claim that drones are quieter - leafblower-ish volume sounds about right. they're noisy.)
A drone, at least, can stay at an inaudible (say, 500ft) altitude for most of it's trip.
A drone could be in your neighborhood every hour all afternoon. There is someone near me who flies theirs at night, i can hear it much farther away than any delivery truck
Just a device to emit the counter sound waves to cancel out the drone itself.
Also, bird flight isn't just "flap wings". Birds have similar dexterity in their wings as you have in your hands. They maneuver by changing the shape of their fingers.