Why do I hear airplanes' engine sounds in the sky? I've been wondering all my life about an issue related to aviation. I see airplanes, large airplanes they look commercial in nature but I'm not sure, flying in the northern side of where I live and where the sea is located. I don't live next or near an airport, there's only one airport located far away from where I reside, about 20 or more Km. But I always hear airplanes flying, the sound of the engine is like the sound of thunder. Sometimes I hear the sound at night, sometimes I hear it at evening and I always ask myself, why do they fly here and at a very low altitude and the airport is just so far from my location? Though, I see the airplanes themselves, so I'm sure they're flying over the sea I guess.
20 km is not that far for an airliner. At the speeds they move over ground, even in approach phase where they move slower than in cruise, they are few minutes from landing or after taking off.

Depending on prevailing winds, the airport might be using an approach path or another. That means some days you'll see airliners overflying you non-stop, while other days you might not see a single aircraft.