Dealing with squeaking screws in chipboard flooring?
A big part of the problem is that the old screws don't have a fully threaded shank. Over time, the screws will allow movement of the substrate. Especially if no adhesive was used between the substrate and the floor joists. A full-thread screw spreads the pressure over the entire length of the screw, with the greatest pressure being applied where it meets the surface of the substrate. I would go back with a better screw, such as a Spax multi-material screw. You might even consider placing them all over your floor between the old screws. My guess is, you will find a lot of other loose screws as well.