I think it's probably a combination of two things. Newer construction not being as good, and people not being as polite. I don't know what the apartments you lived in as a child were like, and I've heard that in the UK, lots of buildings are old, hence better soundproofed, but if you have moved into newer digs, I'd imagine that the level of soundproofing dropped drastically.
Also, once when I was 12, my mother, gandmother and I moved from our house into an apartment to get away from my grandfther who was on a binge and kind of abusive. I remember them telling me how important it is, when you live in apartments, to walk quieter than you do in a house. I was told that every action of yours may be heard by a neighbor and so as to not disturb them, we don't raise our voices, slam doors, or wear shes inside.
That could very well be the difference. I've lived in apartments in my 20's and 30's and people were truly loud, even though I wasn't. I think a lot of it is the lack of manners today, all around.
What I suggest you do is knock on your neighbors door and ask them if you are disturbing them with the noise. Do this to the noisey ones. Tell them that you are aware that the walls and floors are thin, and you know that sound carries and you ask them to please let you know if you disturb them. This gives them the hint that things are heard, but it's done in a nice way where they save face. They can quieten down without you telling them they annoy you. I wouldn't get the hint if somebody did that to me, but most NT's will. I've used that very strategy with a stomper before. She didn't know she walked heavy, and wouldn't have done it on purpose.
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I'm giving it another shot. We will see.
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