[saint_abroad]

Sound decreases by 6dB for every doubling of distance: https://www.airbornedrones.co/drone-noise-levels/

So a typical 80db commercial drone flying at 300m (CAA minimum) would be 50db at ground level (closest point), or about a loud conversation (but less than quiet road traffic).

[Aperocky]

drones noise are very directed, the side noises are much smaller than if directly below.

Source: I did drone noise research a few years ago. It's almost impossible to detect via noise with decent distance (>100m) unless directly under.