When to worry about cracks in ceiling and house making noises?

I bought my house around 7 years ago, and honestly don't know if some of the cracks/noises I'm going to describe were present then, but since I wasn't the vigilant house hypochondriac I am now, they may have been.

I have a strange house, with one part being a super old(well over 100 years) smaller house essentially, with a much more modern expansion added 15ish years ago, perhaps a bit more. When I bought the house there were no mentions of things indicating structural issues etc. from the inspector.

Surprisingly the older part of the house, while it might make the odd noise here and there, and one or two extremely minor cracks, generally hasn't had any issues. Admittedly my bedroom is in the newer add on so maybe there are more noises than I am aware of though.

However in the newer section I quite often hear the odd noise that sounds like a relatively gentle knock, even on days without extreme temperatures or changes in temps.

My bedroom has a couple extremely minor cracks that present as straight lines that are so small you wouldn't really notice them if you weren't looking for them. More concerningly the living room which is a very large room, has a noticeable crack that spans almost from one side to the other.

I did research and know a distinctly bad sign is if the cracks continue to the walls, which fortunately is not the case, nor is there sagging. That room did have a water penetration issue before I bought a new roof, though it is now fully resolved. I've suspected that perhaps that caused it somewhat indirectly(since the location of the crack is not near the area of water penetration itself).

Anyways I was just wondering how normal these types of things are and if anyones deal with something similar, and if they have how did they remedy these cracks, if you bothered to?