I just bought a house that was built in 1977. The upstairs sub floor squeaks. I have tried to put screws in it, but this has not helped. My wife and I have decided to remodel the upstairs and in doing so, will rip out all the sub floor and put a new sub floor in. What should I be looking for when we do this? I don’t want to put this flooring down and have the same problem. I know I will be using tongue and groove plywood, but should I also be looking at replacing cross members also?