I've noticed that the noise level of different quadcopters can vary quite a bit, especially in the sub 3" range. For example, some of the Tinyhawk models are extremely quiet, while other similarly sized builds end up much louder while flying.

I'm currently working on a park flyer build; while I won't be next to anyone, I do expect there to be people within earshot so I don't want to be flying a weed whacker. Rather than just buying props and testing them, I'd like to at least have a working hypothesis on which ones will be loudest before purchasing them.