My flooring–second story, carpeted–squeaks. I tried the scored screws solution answered in this question. I covered the entire room and adjacent hallway with scored screws on all the joists, every 6 inches, per the instructions. After the fix, the squeak still exists, but walking around the room/hallway, the squeak now seems to be more localized–specifically, the sound emanates from the edge where the wall meets the floor. I can walk in the middle or the side of the room and the sound still comes from the edge.
How do I fix (or verify) the cause the squeak? I'm happy to provide more info; but I'm not even sure how to proceed to gather more information.
Best Answer
Squeaking usually comes from two places:
Joists. Loose, overloaded, damaged, braced improperly, not even. Fix is usually lateral support using crosses.
Plywood. Poor quality, warped/damaged, not thick enough, not glued down, not screwed properly or enough, pattern not well thought out (edges should be on joists or supports). Usually have to pull them up to figure out the issue.
In your case you don't want to open up first story ceiling so you need to pull up a couple pieces in high-squeak areas. Figure out what the issue is. If the joists aren't even (note that I didn't say level) the boards will eventually squeak. If there is no cross-bracing then the joists certainly have movement which itself can cause a squeak but also loosen screws or make screw holes bigger over time. These are just common examples. You can keep adding fancy screws every inch but you don't know the root cause yet.