I used to live under a military flightpath used by Chinooks (or else another tandem-rotor craft, if there is any, I didn't look too far into it). Not frequent enough to make it unexceptional and that I never stopped guessing where the beat-frequencied "whoop-whoop" actually was coming from, after factoring in echos off of the house walls (low-density bungalows/semi-detached two-storeys, but still canyon-echoing even after the 'copter rises above a roof or treetop) if I had a moment.
Since then I've also lived for a long time near a hospital that occasionally received an air-ambulance arrival and learnt to aurally differentiate the approach/fly-over pattern of that from the (more frequent) police helicopter, unless perhaps the cops were temporarily scouring the ground near the hospital (normally they covered a nearby woodland, away from the hospital, or some troublesome roads or junctions, notably between me and the hospital, and also don't land for a while). With the windows in the house, and treeline, being inconvenient I probably wouldn't take too much time off to look out into the night sky, after a while, and never go outside especially. But there's still a background fascination. (Two craft in the sky at once almost never happened.) And hearing a Chinookish noise here wasn't uncommon, either, but usually too from overhead to spot above the local effective horizons (houses, trees, rolling hills).
Both places (more than elsewhere i've lived) also had civilian flightpaths for (seemingly!) private helicopters (and transiting police helicopter, to and from other places) and small private planes, doubtless partly because of the handy Road Atlas backup navigation able to use various landmarks.
And then there's major east-west flightpaths and north-south ones, at various high altitudes (some just low enough to be audible, others so high that they're marked only by contrails (Contrails!) or flight-lights primarily visible in the right sky conditions) and I've tried-but-just-failed to get photographic shots of perpendicularly incident planes apparently on a collision course (ignoring vertical separation and suitably skewed viewing angle).
The most attention I paid to helicopters were the two times they gradually came my location in our joint endeavour to observe the Tour de France/Tour de Yorkshire, and were useful indicators as to where on the ground the much-heralded approaching action was, rather than the almost interminable waves of publicity caravan vehicles. Though, the second time, I ended up taking far more photos of the main TV helicopter, above the course across the valley before it doubled back and crossed over to my position, than I ended up with the riders themselves when they finally started to passed me (then, both times, legged it across the respective corners of the course to get closer to the finish-line). The second time, I had a good half-hour or more of view from my temporary hilltop point.
And then there was the time I once saw (and, initially heard) a flight of maybe a dozen or so paragliders, seemingly out on a jaunt, passing over for a good ten minutes or so, in dribs and drabs of slow-moving doubles and triples maintaining some very loose shouting-distance formations (though they probably actually used headset radios anyway, to not need to battle their fan-engines).
((While just finishing writing this, I actually heard a helicopter pass over my current location. Sounded like a typical private flight (not towards/away from the local police 'copter base. And definitely single rotor. I did not feel the need to go to a window. Might it truly be the Age Of Wonder when such an event is not a wonder..!))