Got a similar note. Learned the building rules were posted somewhere I’d never have thought to look — the entrance noticeboard, of all places.
I got a very polite but very firm note about doing laundry on a Sunday, and apparently there are quiet hours I'm expected to just know. It's a whole social contract in the building I wasn't handed a copy of. What house/neighbour rules caught you out, and how did you find out what they even were?