We've had our house for only about a year but it was originally built about 60 years ago. It is a slab foundation and when we moved in, we had the flooring removed to address a leveling issue with the foundation. We knew we would be remodeling and temporarily installed some carpet without any padding, except for in our kids' room, which had the usual underlayment and padding. We lived in the house for about 6 months during which time we sometimes noticed an earthy smell, especially when it was very hot outside.

We were never able to localize it and didn't find any signs of moisture, mildew, or mold. Some research on forums narrowed it to down to probably crack(s) in the foundation that brought out the earthy smell when water evaporates. We thought the carpet wasn't a very good barrier on the concrete. And we thought all would be properly addressed during the remodel (renovation and addition).

Fast forward another 6 months during which time we lived in an RV, redid about 90% of the house, and added a few rooms.

Recently we've noticed that one wall of the same above-mentioned kids room has a strange smell, most noticeable around the light switch. When we removed the electrical plate we discovered a strong smell inside the wall. Smells are so hard to describe... It is also an earthy, musty smell but also has something slightly chemical about it, like we've tried to address the musty smell by masking it, which we haven't. We can't say for sure if it smells like mildew. (Whereas the smell from before the remodel did not seem like mildew at all. So actually it may or may not be related to the old earthy smell.) Or it could be an earthy smell mixed with the new building materials.

This wall is complicated. It used to be an external wall with an old aluminum frame window in it. During the remodel, the exterior portion of the wall and stucco was completely removed. New concrete foundation was poured for additional rooms so this wall is where the new and old foundation meet (but no smell from the floor in the doorway of this wall where carpet meets hardwood). It is also where it "joins" with the new roof, although the new roof is about 1 foot higher (ceilings are higher in the new room).

The window was removed so some studs were added. But overall, the old studs remain. There was no sign of mold, rot, or damage to the original wall. The old interior drywall wasn't replaced (except to close the window) and new 5/8" drywall was added to the other side.

We've read other threads about musty smells which seems to indicate that it is somehow related to moisture. We were thinking we could put things inside the wall to pull out moisture and the odor but we don't want to discover water damage years later. Is that a real concern? Could this be leftover moisture trapped from the construction during wet winter months and once it "airs out", we'll be ok? Do we need to somehow insulate the wall, but from what?

We've been back in the house for 2 months and after the huge remodel having to think about home repair makes me want to tear my hair out. But this wall is between our children's bedrooms and we do not want them to get sick. Our contractor has been back and verified he does smell something but has no clue what it is. We don't even know where to begin. Please help!