It has not rained here in like two months but my basement smells so musty. The house is over 40 years old but the smell comes upstairs and you can smell it all the way at the top of the basement stairs and into the kitchen. WHat is the cause? I have a dehumidifier running, but is there a reason why it stinks so bad down there? The basement does not leak. Although when it is very humid out it smells even worse. Any suggestions?