For over a year our dining room and guest room (directly above) has had a strange odor that comes and goes. The smell always lingers but varies in intensity throughout the room at different times. The smell is difficult to describe but the closes thing I could compare is dust on a lightbulb or burnt hair, but much more intense. We had pest control come and they said it was not a dead animal or rodent. An electrician came to examine and could not find anything wrong. The furnace and vents are clean and the scent does not seem to be coming from that area. Both individuals doubted it was a mold smell. Any ideas? Neither even had any good advice as to who to ask next. It is costing a lot o money!!