Can anyone advise us on an odor we have in our basement? This smell permeates both sides of the room (divided into rec room and utility area) and at times is noticeable in the rest of the house from around the basement stairwell. We've been unable to identify either what the odor is (could be musty, mildew or mold, although there are no visible signs of mold or mildew). We moved into the house a year ago, and noticed the odor when we first looked at the house, but thereafter the owners seemed to have gotten rid of it. They had previously had a basement flood (signs of water damage on carpet, etc.). Our home inspector did not find any signs of moisture and said the sump pump was ok. The odor has returned. We have a dehumidifier running 24 hours a day, and there does not seem to be any sign of wetness in the basement. What type of contractor would be the best person to call to try to find out what is going on? If it is coming from the sump pump or crawl space, should we be treating the sump pump with bleach or some type of cleaner? I know this is a very broad question, but any ideas/suggestions would be most appreciated.