So I would recommend you guys change the project name / goal to
Low Noise Profile Quadcopter
or something along those lines. Anyone who heard a quad copter in real life knows as the throttle kicks up, they’re loud as hell haha, there’s only so much you can do to cut down sound coming out of those motors, it will never be “Noise-less”.
Very large props plus very low KV motors will get the sound down, and a frame made of thin plastic or very thin titanium to cut weight will help also, but I’m almost certain it’s actually not possible to make it noiseless, unless by noiseless you mean you can’t hear it from let’s say 50 yards away.
Anyways, thought I would throw that out there so the project can have a better , more realistic, chance at success. Quads are loud, so if you significantly can bring down the noise levels, even if you can hear it, that’s still a great achievement.