How do I repair the sub floor?
Ive made a lot of repairs of this type. You may actually have two scenarios happening here. First, as you mention, the subfloor itself is warped. This happens easily when the subfloor is partical board, less so, when it is OSB, and only occasionally with actual plywood. If this were only a mild hump, I would recommend simply resecuring it to the joists. This could be done by screwing right thru the floor (since you are going to recover the floor), or by working from underneath – by installing a Squeak Ender bracket (link provided below). Ive used a lot of these over the years, and they work very well. Since yours looks like a ‘tree is growing up through the floor’, hehehe.. then I’d say you need to replace the subfloor. I would mark out a square larger than the hump, and cut it out with a circular saw (set the saw blade depth to the depth of the subfloor, which you can find out by drilling a 3/4″ hole thru it, to measure it). Run the saw around the perimeter of the cut, and pry the sub
