Search your house high and low for anything that might be rotting. They could have created a colony somewhere in your house. I had this happen before and I was ready to bug bomb my entire house until I found a pumpkin in the basement buried under some flattened cardboard boxes. It was the most disgusting thing ever! The smell was masked because it was next to the laundry room which smells like detergent, bleach, and fabric sheets. Good luck!
I'm thinking if the neighbors on either side have rotten wood under their trailers, this might just be a long term maintenance thing. My right neighbor says her back bedroom smells like mold. *sigh* She's not right up on us: you could hit her place with a rock but you'd have to throw it pretty hard. LOL (Same with my bestie on the left) Our Slum Lord fixes nothing unless it's a major appliance or water heater, so... *shrug* At least they're not going to be in my token house plant anymore. ::is happy!::