I have helis flying over all day every day (bar Sunday), being under a major helicopter flight path. We get the odd plane or light aircraft going over too.

I was sat wondering wtf a droning noise was - too quiet for a heli, too low a tone for a commercial aircraft - looked online at it was the US Navy heading up to Norway for whatever reason.

The Eurofighter Typhoon has a real unique engine note too, even at a couple of tens of thousands of feet up, it still makes you wonder “hey wtf is that sound?”