It doesn't happen all of the time(I guess it could but we're not in his room much to notice) but when we're in my son's room and the A/C comes on sometimes it has the worst smell. Almost like a dead animal. We had squirrels in our attic so now I'm wondering if one of them died and is causing it to smell. Can they get in your duct work? The smell doesn't come out of any other vent in the house, even my daughters room and that's next to my sons.