For months, Evan Porter ignored the small dip forming near the edge of his backyard. At first it looked like nothing more than uneven settling, the kind most homeowners deal with after heavy rain. But as the weeks passed, the soil continued to sink in the same exact spot, forming a shallow depression that kept growing.
He tried filling it with fresh soil twice. Each time, the earth sank again within days.
One morning, while mowing the lawn, Evan noticed the depression was now almost two feet across and soft enough that the mower wheels dipped into it. Concerned that there might be a broken pipe or some kind of burrowing animal underneath, …
They chalked it up to old-house quirks until one evening, as they were folding laundry, the floorboards gave off a faint but unmistakable knocking sound.