Go ahead and post the sound recordings they may or may not be useful but we will never know if you dont.
There are no pipes in this wall. Its not water knock, I believe. It sounds structural. It happens when the person above me in the apartment next door (3rd floor, I am 2nd) walks around or moves around her bed near the wall. I know this because I asked the apartment manager what is in that room above me and next door. Thats what the manager told me.Heating pipes expanding and contracting in length each time the boiler cycles on and off and, when passing through a tight hole in the wood framing, they stick and slip with small noisy movements. (?)
Go ahead and post the sound recordings they may or may not be useful but we will never know if you dont.