I spotted this in my laundry room the other day; the wall felt a bit spongy behind the sink. After cutting out the drywall, I found black mold creeping along the insulation where a slow drain leak had soaked the studs. It smells musty, and I'm worried about it spreading further into the walls. That hidden plumbing crack is really the culprit here. mold behind drywall near plumbing 41