The sound of crickets or writing "crickets" implies silence. As in, "Anyone want to volunteer?" *Crickets*
Well, yesterday afternoon, I walked around on my floor and I heard... cricket. An actual cricket outside (apparently fulfilling his duty to indicate silence). And that's all I heard. No more noise from the floor! :D
Even better, fixing the problem turned out to be much easier than anyone expected. The handyman cut out a small piece of the subflooring over the area where the noise seemed to be coming from. Looking down, he could see the piece of 2x4 wood which sits on top of the metal support beam. He pushed down on the 2x4, and we heard the noise. That 2x4 was the culprit!
No one had suspected it because normally that 2x4 would be pressed tightly between the support beam and the floor joists, with the weight of the floor holding it firmly in place. But in this case, there had been a wall in the basement pushing up on the floor joists for many years. Over time, that upward pressure had loosened or bowed the 2x4 a tiny bit.
The solution was to tap in shims between the 2x4 and the beam. Two shims and the noise was gone.
The handyman added adhesive, replaced the cutout piece, and screwed it down. Done!
I had used three tubes of adhesive, three packages of shims, and 87 screws trying to silence the floor. I spent hours spent gluing and shimming and driving screws. I endured months of frustration. If only I had known what the problem was, I could have fixed it in about one minute with two shims.
But you know what... strangely enough, I don't even care. I am just overjoyed that the floor is silent.
I have already begun installing my new flooring. :) Hooray!