Not long ago I made a recording of noises coming from the toilet (sounded like water rocking where the water is collected). As soon as I laid the recorder on the floor (it made a 'tic' noise) it stopped. I still have that recording.
I think maybe they are trying to bully me into getting out of here. Maybe they want the apartment. Maybe also they want to make me believe in something supernatural.
It could be that their strategy is to instigate a fight between neighbors. The usual thing to happen is that both parties involved get blamed (even though in this case one is clearly in the right). Then they can make the fight escalate until you withdraw and go live somewhere else.
They're maybe also trying to get the ground here, to build more expensive living or shopping buildings.