We’ve been having this issue with a slight smell in our basement laundry area and no idea what was causing it. We have a cat and we had changed the cat litter a million times to no avail.
T discovered what it was this morning. A dead possum under our deck outside our laundry room windows. Every time we ran the dryer, the air “steamed” it and well, you get the picture! I am glad it is winter because at least the cold kept it from decaying even more.
Now, T has the delightful task of removing the snow from the deck, removing the deck boards and retrieving said dead possum to dispose of it.
Glad it’s him and not me 
Home ownership at its BEST.
Oh, yeah