We built a modular house, with a full unfinished basement, in Western MA in 2005. The house has been developing an odor throughout the upstairs and also in the basement. On the advice of the modular company we sealed and painted the concrete walls and floors in the basement and that has done nothing to eliminate or ameliorate the odor. We installed dehumidifiers and air purifiers, again to no avail. The smell appears most prevalent upstairs when either air conditioning or heat comes through the floor vents (the smell almost seems to travel up through the ducts), but at other times as well. Any ideas and recommendations?