Ideas
I had a similar thing happen to my sims today. I started a new game on a new computer (no mods, no cc). At first I had a good gnome show up to clean. Eventually it sopped moving around but was still making the moving noise. So I sold it. I then got another one, that was a protector gnome. This one didn't move about, but did make the noise. I left that one be but then got a bunch of destructive gnomes. They stared wrecking the place but the other gnome did nothing. I ended up deleting the lot of them. My sims have had no ailments. There luck has been high. The only thing that has changed, is they now have an infant. They also get moods from milestones they have never had. I have all other expansion, game and stuff pack installed and most of the kits. I am not playing in the new world and my sims are doing the painting career and the Eco career.
The picture is of the first gnome, that was apparently cleaning.