Yeah, I had the same thing happen to me twice (in two different households). If you're sure that the moodlet really is stuck, and that it's not just some trash, or spoiled food hidden in a corner somewhere, or in your inventory, then you'll probably have to do what I eventually did and buy the Lifetime Award that resets your moods. It's ridiculously expensive, but it's definitely gonna work.
I noticed my flamingo lawn ornaments were classified as knocked down even though visually they were standing upright. I had to get rid of them completely before the mood thing got taken off. Maybe there are other small things like such that could do it? --- Sub Zero: You are somewhat distant (some might say "cold"), preferring to conduct your business on the DL instead of attracting a lot of attention.
if your sims has a clean trait they will find dirty to complain about but then there should be a clean house option that will clean every dirty room in the house. if nothing else it sound like you need a clean sim in the family just for this one reason.
Check all your decors. If any one of them gives you the option to "Replace for $XXXX", that's the culprit.
I had a fire broke out from the fireplace, which my Daredevil sim quickly extinguished, but everyone gets the dirty moodlet whenever they go near the fireplace after that. No amount of "Clean Entire House" fixes it. It took me a long time to realize that it's one of the decors on the mantel that has to be replaced.
I know this is a couple days old, but had the same thing happen to me. Turns out a door was blackened from a fire, since I play in the Wall Cutaway mode, never saw and it was really annoying. So a suggestion would be to put the walls up if you still can't see anything. Perhaps you have a broken window or something.