We have a walkout basement with sliding glass doors. during the winter months when we keep the doors closed there is no problem with odor. But, anytime we open the doors for any length of time we get a strange odor that fills the basement. My wife thinks it is cat urine smell from the carpet. But why would it not smell when the doors are closed? Others have said it may come from under our lower deck that is built off the glass doors about 1 foot off the ground. Can anyone help us solve the mystery. I have put carpet deodorizer down and it helps conceal the odor but no fix. Any ideas?