House smells of mildew

[Gail W.]

     I recently bought a house  for a rental. We noticed a smell when walking through the property that was something like mildew. The house was owned by an elderly couple and after the owners passed away it sat empty for about a year. The estate sent cleaners to the house and they shampooed the carpet among other things. The carpet was wet when we did our walk through. After painting most of the walls and cleaning our selves I placed a tenant, who commented on the smell. I told the tenant that the house had been empty and shut up for some time and after cooking and doing laundry and just living in the house the smell would go away Well it hasn't. The tenant is concerned and so am I. I have been in the crawl space and it is mostly dry. Also we had a home inspection and no mention of this.

     I wonder if anyone has dealt with a thing like this and if I could get some suggestions?