We have a similar problem -- a smell we cannot place -- in a corner of our home and in attached garage on the same outside wall. It seems to come from wall outlets, not floor or ceiling. We removed drywall and insulation, down to the brick. We first thought it was a mouse or dead skunk, no avail. A pest control guy said he thinks it is a dead snake somewhere -- that their smell lasts years. (A mouse supposedly only smells for a few weeks...) We still have not found it and it is hard to describe, but it carries strangely through the lower level of the house, especially when it is damp, raining, or windy outside. The brick wall and foundation is intact on the outside of the house.