quadcopters are pretty quiet if they are flying at a good distance, it's only the ones zooming in that are loud.
Just be as far away as you'd like an actual highway, but in this case vertical space works too.
Just be as far away as you'd like an actual highway, but in this case vertical space works too.
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).
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.