As an add-on to south-40’s, did you check other places, like the chimney, the bathroom exhaust pipe, the furnace exhaust, the attic, any place where a squirrel could have climbed in?
Yeah I checked every thing. the smell is strongest in the wall between the living room and den. I betting it’s a squirrel, I found out that it rained pretty bad last week and all of the clocks were flashing when we got home so I’m betting that it probably can in trough one of the attic fans while the power was off and either fell or gave birth and the babies died.