We have an infestation of tiny gnats that congregate right where the wall meets the cieling and just inside the window frames (both at the very top and along the bottom). There are no plants in this room and the room is on the 2nd floor. There are plants elsewhere in the building, but not this room. No obvious water leak anywhere. I vacuum them away only for there to be a hundred present a few days later. There is an AC vent near the base of the window but I haven't noticed any more near this vent vs anywhere else in the room. How to get rid of them completely? Is it possible that they might be breeding in a plant somewhere else and are attracted to this sunny room? I have checked rooms w plants and can't find any tiny flies (maybe one or two, not tons like here).