musty smell in basement foyer

There is a musty smell emanating from the foyer at the bottom of our cellar stairs in our rural house in Chapel "Hill NC. The smell is localized and we do not smell in the basement. We have bleached floor, cleaned walls and treated with SCOE. We have vented the house several times with house fan but it still persists. It is not an obvious mildew smell or dead animal. There were some dead millipedes near the space in the basement that smelled very bad but we removed an cleaned and that area is just fine now. Any thoughts on what else we might check would be appreciated.

Many thanks.

Have a inspector check for moisture in that area,

Have a limited mold inspection performed which would inspect for moisture and include an indoor air test (mold test). Should cost about $350 - $500.

Also bleach does not kill mold on porous or semi-porous surfaces such as a wood.
Tell us what area of the country you are in, and we might be able to recommend somebody certified to look at it for you.