It’ll be ok Baku. Unfortunately I have been creeped out by sounds which then triggers your mind to everything as you try and sleep and you’ll overthink things.

The noise could have been anything including possums or something or the pipes but it’s not going to make you feel any better about it for awhile.

Best thing to do is to try and put on some relaxation sounds or a podcast/audio to fall asleep with or if you have earplugs that would help.

That does sound creepy. Maybe the metal of the latch shrunk in the cold, and you heard it fall open?

Maybe it could have been pushed shut with a broom if one was available. I’m not familiar with manholes. But definitely do what feels safest and stay in your room.