I had a different problem. In this appartment that me an a girlfriend were living in, the layout was such that the wall separating the two appartments was between the bedrooms.
Well this one guy moves in next door sets all his shit up, then leaves to fly back to his home country to go get his family. Problem is, he didn't set up his alarm clock or something so around 1:00 AM his Alarm goes off and no one is there to shut it off!!
First night, I pull the top mattress into the living room and we sleep in there. Next night, same thing, so I wake up the landlord and tell him something has to be done.
Third night same thing, so at 2:00AM I wake the landlord up again because the guy still isn't back and tell the landlord if he doesn't go in that appartment and pull the plug, I will bust the door down and do it myself. Needless to say, the landlord complied.
Point is, other than me getting to vent about it, is that you have to be firm, and if that doesn't work, you have to get mean and do what you have to do. Are you worried about getting your ass kicked or just worried about being known as the party-pooper if they know it's you? Because a decent nights sleep is more important that what people will think of you.