I have owned my house for about a year now and there has been a dead animal smell off and on during this time. The first time it went away I was relieved thinking it was over, however several weeks later it was back. I cannot find a leak, a dead animal or any clue to the problem. I know there is something causing the problem because numerous large flies appear every time the odor returns. This weekend I even cut into the sheetrock to see if I could locate the source and nothing... I don't know who to call - any suggestions?