Oh yeah those things too.
I spent hours, and I mean hours searching for a coughing child that sounded like he or she had a case of pneumonia. The cough was so loud I could hear it miles away. Eventually I found the sound-producer. It was a tiny, triangle thing tucked under a building. I had to go to grid view where I saw it. I then moved the building out of the way and deleted it. I had a bunch of others too on the route that drove me crazy as well all similarly tucked under things, making them difficult to find.
Not sounds, but similar. Watch out for geese or ducks. It's a nice asset of geese or ducks flying around. The asset its self is a tiny triangle with the birds attached. The problem is you don't see the birds when you first place the object so you think it doesn't stick so you place another, then another, then another. When you finally see the birds flying around, it's like gigantic gaggles of geese. Once played, these little triangle bases are difficult to find and click on so like sound use them sparingly.