I bought a "squeeeak no more" floor repair kit to eliminate squeaky floors. The kit has a joist finder that you use to drill through the carpet and plywood to check if there is a joist underneath, and go from there. It worked really well in some of the rooms. However, in some other rooms, the joist finder did not work at all. It simply could not go down below the plywood. I pulled the carpet to see what's there, and it seemed like plywood but the joist finder could not drill through it. I've attached an image. I tried several different spots in this room but experienced the same problem. Any ideas why joist finder cannot go through this floor and how to solve this issue?