I have a newer side-by-side condo, and the first floor is an open floor plan between the kitchen and living room. The second floor hallway goes right down the middle of the house right above the space, and the floor creaks something terrible. Before we recarpeted the second floor, I tried fastening the subfloor to the joists with 2 1/2" screws (or thereabout). It does not appear to have helped. My suspicion is that it's not the floor creaking; rather, it's the walls that are fastened to the second floor floor. It seems as though when we walk in the hallway, the floor flexes down, the wall stays put, and the fasteners squeak. Am I correct in this theory?
If I am correct, what would be the best way to remedy the situation? If I re-fasten the wall footer to the floor joists with screws, my concern is that the heads will pop off or worse, it will start pulling the wall down and cracking the drywall. Based on an ask-this-old-house episode that I saw recently, it kind of sounds as though the second floor joists are missing the blocking/bridging in that area.