This may be horrible advise but they are doing this because they can get away with it. You back down everytime they escalate things and they know it. They are afraid of consequences because they stoped the floor vibrator incase they got sued or the police came just not from you.
You need to stop backing down record the noises, get security cameras that record 24/7 if you can and get evidence to give to the landlord or the police.
Better yet get a family member or a friend who doesn’t mind conflict to hang out for a few nights a week and have them go and talk to them whenever they pull this bs. After a few times they will back off. It’s better to do this yourself but it sounds like you need to work on your confidence before you can do this yourself.
The closest I ever got was saying something like that at customs. The Border guard asked me “Why are you coming to the US?” and it was 3 years into Trump’s first term and all I could think of was “Because they pay me to.” He laughed and waved me through.