Sounds like a combination of moisture and restrictive air movement. If this is normal humidity, I'd paint these surfaces with paint that had an additive in it to hinder mold growth and leave a little more room behind the refrigerator and benches.I live in a walkout ranch with an attached garage. I access the garage through a the basement door. When we rearranged our work benches we discovered mold on multiple surfaces as well as on the refrig, speakers, etc. Any ideas?