I've heard those things and they often sound like a pissed off weedeater.
You have no idea what you're talking about. A passing car is louder than a small, well-tuned quad with quality balanced rotors at ground level. 30' in the air? Barely audible. There are noisier ones. I work with a 25-pound octo that sounds completely horrifying, and I know when and where to operate it. But thanks for speaking out of ignorance - it helps to put all of this stuff in perspective.