Six months ago, we bought a 1942 Cape just across the street from a reservoir in Hamden, CT. The house is in great shape, but we've had one persistent problem that no one seems to know how to resolve: whenever there's a significant shift in the temperature outside, a sour smell comes from the pipes and drains in our basement and in the second floor bathroom. The odor persists until the temperature outside stablizes. We've had a few plumbers investigate the situation, but no one can tell us definitively the cause of the rancid smell. Most agree that there is a particular area in the basement where the smell seems strongest, but so many kinds of pipe intersect there (old and new, water pipes and gas pipes) that the originating source is hard to determine. We're now faced with the prospect of moving forward with a list of possible "repairs" that we're told are not only expensive but also may or may not take care of the problem. We've been advised against having smoke run in the lines because we're told that it is an expensive procedure that will likely provide inconclusive information. Anyone had this kind of smell problem? Anyone have any suggestions, thoughts, insights, solutions, or caveats?