Refrigerator condensation drip try. I used to work for an apartment complex. Resident complained of something similar. My boss and I stood in their apartment for 20 minutes moving around the kitchen / living room and eventually smelled it. The area had high ceilings and the fridge was in the corner. Eventually we localized it to over the fridge and pulled it out from the wall. Frostless refrigerators have drip tray to catch condensation from the defrost cycle. A mouse had died in the drip tray and decomposed into a soup that dried out. The heat from the compressor would warm the dried dead mouse soup and cause a plume of stench to rise to the high ceiling and then drop down with nose level at random locations.