Musty Smell in slab and block house
My sister had a condo and had very similar problems with the odor. It was the a.c. ducts actually installed in the ground with the foundation poured over then. They rusted out and that's where the musty smell came from. We ended up filling in the ducts and sealing them and running some new ducts on the ceiling and framing around them with drywall. If you have registers in the wall that might be why you think the odor is seeping in from them. Good luck.