Hmmmm, you guys are trying to solve the problem in the wrong way. If they are so inconsiderate as to disturb you in the first place, they are not going to listen to your protest for very long. They may even turn the noise up a notch just to get their own back on you. I successfully solved this problem a few years ago when my doped up neighbours refused to turn the music down at three in the morning.
OK, here is what you need to get hold of or buy.
12 ft of fish tank air tubing.
1 fish tank air pump that has a in and out nozzle for the tubing.
1 large gallon bottle
1 wine makers rubber bung with two metal outlets.
1 ten inch masonry drill that is the size of the fish tank tubing.
Some Blue Tac
OK, wait until the offending neighbours are out then make a small hole in the wall through to their apartment in a discrete place where they will not notice it.
Measure, cut and attach the tubing to the hole in the wall (sealed with blue tac) and to the out side of the pump.
Measure, cut and attach the tubing to one of the metal pipes on the wine makers rubber bung and to the in-side of the pump.
A quarter fill the plastic gallon bottle with fish guts from the local fishmonger and put the original cap on before leaving it for a week. When you smell it, it must be very strong and disgusting.
When it is ready replace the bottles cap with the rubber wine makers bung and you are ready to go.
OK, without saying a word, you wait until they turn their music up loud and simply reach over and switch the pump on. When they turn the music off you turn the pump off.
The will have no idea where the smell is coming from but will be conditioned to not play their music so loud.
If they complain to you, invite them in and say, it must be your drains because I don't have a problem with horrible smells in my flat.
Job done, my noisy neighbours moved out within a few weeks.
Remember, always smile and be exceptionally polite and never let on its you doing it or threaten them with more smells. lol let them learn the lesson the hard way.