I have a putrid odor coming from a single cold air return in my bedroom, which is located on the 2nd floor of my townhouse. It smells much like a decaying animal. I have just had all my air ducts cleaned by a professional this morning, and he assured me there was no dead animal in any of the ducts. We lifted the carpet and underlay near the cold air return vent to see if the odor was coming from the subfloor - nothing. On the other side of the wall is the main bathroom, where my son bathes, and makes huge messes of water on the floor. I thought perhaps it might be mold and bacteria from the water seeping through the flooring and between the walls. Yet, the smell is also present in the basement, 2 floors below, in the same corner! There is no smell on the main floor of the house, anywhere, although the putrid odor is starting to make its way through the rest of the house as the day wears on. I am trying to mask the smell with deodorizers, but it only seems to make it worse... :mad:

Try running a Dehumidifier in the room that has the strongest odor. It is possible that water is present or has come in from the outside.