The "Dirty Surroundings" moodlet keeps showing up for my sims, even when my house is clean. I use the maid service, and the maid has nothing to do, so there isn't anything to clean.

my only thoughts are this:

1) Bad plants in the garden that I haven't seen
2) A meteroite hit early in the game in my lot. Could it just be the... stench of it?
3) It's a part of the Unlucky trait.

That's all I can think of... any other ideas?

Maybe you missed some burned objects from when the meteor hit? Take a look at every object, including small decorations and stuff on the walls.

Maybe you could hire a maid, have her clean once, then fire her.

There is a mod that unlocks the "clean house" interaction, but I don't remember when I got it. I just use that when I don't know what's dirty.

It's a mod made by Buzzler http://www.modthesims.info/download.php?t=411634

Bingo. When they land they cause MASSIVE collateral damage, blowing out windows and 'tainting' anything within the blast radius. I damn near bulldozed my house trying to get rid of that moodlet. Turned out I had to replace some windows and outside lighting before the it would go away.
So wherever it landed you'll have to do a very thorough check of the area, right clicking on anything and looking for the 'replace' option.

Thank you! That is exactly what it was! Didn't even think of looking at the windows.

Yeh i had a rather annoying "Dirty Surroundings moodlet that stuck and wouldn't leave after a meteor hit my lot, Eventually i discovered a couple small things that were still damaged i replaced them and it went away then, Personally i hate them meteor's.

I had the same problem and found it was the cat scratching post that needed to be replaced. That fixed the problem for me!