I have a squeaky floor and I'm trying to use a kit to screw the subfloor to the joists. However, while drilling to find the joists I can go down less than an inch before the drill stops going down and instead makes a noise like I'm drilling into concrete. The room I'm in is at ground level but there is basement below it. Would there be any reason for a cement-like level under the subfloor? How can I know if it's safe to fix the squeaks?
Update: I'm fairly new to home repair. I just bought my first house a few months ago. Anyway I pulled out a vent and didn't see anything too out of the ordinary. It looks like there might be two subfloor layers, one particle board and one plywood. It's possible I easily went through the particle board and I'm not used to how hard the plywood is.