Im sure its cast iron, examine it and where the pipes join. This time
of year rodents look for a warm home, If it is a dead animal in a
week or 3 it should smell less, then go away. I just poisoned a bunch
of chipmunks, maybe 20. I hear them dying in the walls. Im not looking
forward to the next month. But it will pass, or ill take a vacation.
Sewer gas smells well like crap . dead animals are real foul, you say
its getting worse, and like garbage, sounds like an animal, but it will
dry up then go away. put out some traps, you have more, if you have
one. They are a bundle of fun.