I recently bought a new split entry house with a full finished basement (6 months ago) and since I moved in, it smells musty in the basement. Being naïve, I thought it was normal for a new house to "dry out" and it would simply go away. Not true, after about 2 months it got worse and we found some mould growth on the baseboards of the exterior walls... behind the sofa, underneath the toilet, behind the headboard of the bed, etc. I cleaned the mould off and purchased a dehumidifier with a relative humidity readout. The RH was near 80% and we pulled about 3 gallons of water out of the basement. We thought that the problem was solved as the RH is below 50% all the time and we haven't seen any mould since (2/3 months ago). However, there is a corner in the basement that smells like old clothes that you would find in your great, great grandmother's closet and it is coming from the electrical outlets. My builder and I pulled off the baseboards along with the drywall and could find no sign of anything but the smell. Could it be that the concrete was curing and releasing moisture where it condensed on the cold walls to form mould? And could we simply clean the carpet to get rid of the smell? Or should we get a professional to do mould samples? Any suggestions can help!

If they used conduits for the electric and the conduits filled with ground water it could cause this.

Mold, being a plant, needs water. Having been in construction for 24 years, primarily drywall and also taking a course in mold remediation (sorta necessary in Florida), it sounds to me as if you may have a water source (however small). The dehumidifier can't compete with a leak; as it will continually remove the moisture that a possible leak is continually bringing into the room(s). Once a material has grown the fungus, the only solution is removing the material completely or treating it with fungicide. (using bleach is a myth concocted by those who want to make good money from the misfortune of another). You may want to call a remediation specialist to see if the spore count indicates a continual supply of moisture. It's not an easy fix and my heart goes out to you.