My basement is pretty musty. It's finished and carpeted and our cats' litter is down there, making for kind of a perfect storm of stink. The problem (other than the stink down there) is that any time the AC comes on it spread the smell through the whole house. I can immediately smell it coming up from the vents. I don't think it's an issue with the vents themselves since (1) we had all our ducts cleaned 2 years ago when we moved in and (2) any smell that's down there comes up, not just the musty smell. My husband once bought scented litter by accident and our entire house smelled like it once the AC came on. Our system is down there and one of the intake vents (I think that's what it is) is located at the floor level, right in the smelliest part of the area. Is there a way to stop the intake of air from down there?