Originally posted by DragonIV:

Some of the crypts are positively huge. It's not hard to miss a room in them, and if I'm still hearing draugr or slimes splooshing around, I always end up finding a missed room.

I have a practice of always following the right hand wall (in any game where there's no map for locations like this).

So, in these crypts, I only mine what is to my right, and if it opens another passage, I follow that even if there's more to mine right there in that same room. I'll get to that once I wrap around, eventually, and it's on my right.
Doing the sunken crypts like that, it clears the entire crypt without there being any actual opportunity to 'miss' anything, unless there were secret doors. That's why I asked. There is zero chance I missed anything that was not hidden.

It seems it is loading the other nearby crypts when you are underground, btw. I cleared the last of the crypts in this swamp area and returned to the previous one where I was hearing the draugr noises. It's now quiet there (other than the sloshing, which appears to just be part of the background audio loop).