[yellowbkpk]

It depends a lot on the wind and the size/shape of the propellers. When I fly my DJI UAVs up near 400 feet above ground on a zero-wind day it's very easy to hear when I'm outside. When they get to be ~500 feet away it's much harder to hear. I've never been inside while flying, but my wife says she can't hear it when she's inside. On a breezy day, the wind through the trees covers most of the noise while I'm outside, but the variation in the noise when the flight computer is compensating for wind makes it a little easier to pick out.

Bottom line: you'll probably be able to hear these large Amazon UAVs when you're outdoors and when they're within 500 feet of you.