Steve, thanks for the comments. No, I have not had an unusual amount of rain this year. The basement is finished. I do not have any crawl spaces or a way for an animal to get into the house. Good suggestion because the smell does remind you of a dead animal. My house was built 3 years ago and this problem started to occur the fall after we moved in. I think the odor is related to the moisture in the ground but I do not know what is forcing it into the basement.