Are you sure your smelling a mold smell, or is it more like a damp
Because I worked in greenhouses for a good portion of my life and come
from an area that is predominantly full basements and recently moved
to an area where most of the homes have dirt crawl spaces underneath,
perhaps I noticed the difference more easily than most.
Almost every home in this new area I live, if the room is not
ventilated (heated or cooled), to me, it has that definate damp earth
smell, that people who live here don't easily recognize and think its
If you have access to an ozone generator, perhaps you could put that
in the room (unoccupied) for a few days set on high.