Strange smell in August only
Could there be a hidden floor drain in the area? It wouldn't explain why the timing is so regular, but it might be connected to something that does. I've dealt with a similar come-and-go odor problem in a commercial buidling that ended up being a 4 inch open floor drain that was just carpeted over when the building was turned into offices. That drain line connected into a drainage system that was tied to a nearby building that housed a chicken processing operation. You can imagine what sorts of things were washed down their pipes. It typically only smelled during the dry season, I suppose because some elbow trap between us and the odor dried out.