There are so many factors to be considered here that it is impossible to answer.
In very quiet conditions, with no wind, no traffic and nothing to block the path of the sound, you probably can hear your drone from hundreds of meters up. Close to a freeway or the sea or with wind blowing through trees, you will not hear your drone if it is more than 10 meters up.
Is there any data on noise contour profiles for a spark or other drones? Like the ones they have for commercial jets for airport developments but in miniature! I've also wondered how far away the spark can be noticeably heard from a discretion point of view, not just vertical but lateral distance as well.
I don't think this data is available, simpy because there are no regulations regarding noise from drones so there's no need for such a profile.
However, with enough time and with the help of apps on your smartphone, you could create these profiles yourself. Download Phyphox or Science Journal for your android phone. They both allow you to measure sound-pressure. Found a quiet spot and time, lay out a grid, have your drone hoover at a couple of meters and measure the sound level on each grid point. It should then be possible with some clever arithmic to construct a sound profile.
In fact, I might do it myself, sounds fun!
Don't be silly, I have never seen a visible sound! But would love to.
I have however seen photos of aircraft breaking the sound barrier.
So if you are totally deaf you will not hear a sound, I find that my spark's sound gets softer from about 5 meters up and gradually diminishes the higher it goes but at 40 meters I can still make it out if all other sounds are quiet, but in a noisy area.... nada!