There are 5 blocks of 2 flats each where I live. To get to my flat you have to go up a flight of stairs . Fairly regularly I hear the sound of someone knocking on a door. Every now and then I’ll open my door to check if it’s someone at my door. There’s never anyone there.
My granddaughters and cleaner knock on my door ,but they make it clear when they’re coming.
I lived in a place like that. People knocking on other people’s doors sounded like they were knocking on my door. Sound used to travel all over the place.
I hate sharing sounds with neighbors. Always hear a cell phone beep. It’s not mine. I hear them having sex. They hear me making raps. It’s irritating for both of us .
I’m not discounting that possibility. There are 5 blocks of 2 flats each here . To get into each block you either have to know the code or buzz to be let in . I’m not sure whether I’d be able to hear someone knocking on one of the front doors in the adjacent block.