Here�s what we�ve done already to try to target / eliminate the smell:
We ripped up the old carpets and carpet pads
painted all of the walls
used glade plug ins
bleached/cleaned all cabinets and surfaces
removed appliances
had septic emptied
sealed any possible entry for mice or other rodents (easily accessible before we bought it)
removed appliances
gutted bathroom
removed subfloors in kitchen area
Potential Sources: The previous owner had cats. There was definitely rodent infestation when we bought the place, but we did what we could to try to prevent them from reentering the house. My guess is there are dead mice bodies in the walls, but would that continue to smell months/years later? The ducts have mice dropping in them still.
The basement could be the problem, when it rains a lot, the crawl space gets damp and there could be standing water after really heavy rains. It will eventually drain to the sump, but the concrete floor will remain damp until we have a period of dry weather. I�ll be setting up an auto drain dehumidifier tomorrow that removes 70 pints/ day.
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We are going to the house tomorrow morning and need some good ideas to try to get the house smelling better for when we re-open it in April.

Anyone have any thoughts or advice that might help? This has been bugging the hell out of me. We want to enjoy this place in the summer and having it smell the way it does will not allow us to.
Thanks in advance.