What if over the years sense humans died drones evolved more ways of comunicating with eachother. Sense their regions seem to echo a lot they devolped small noises such as pings, ponking noises, a strange wheezing noise, trilling, clicking, and small very short screaching noises that some how bounce off the obstacles better than anything and can cary for miles for just a small noise.
So if humans did come back for what ever reason or however reason they would hear a chorus of beautiful noises echoing all around them. Like large flightless wingless metal birds all letting off their small noises at once, it al swirls in the air and makes the dead planet feel just that more alive














