I feel sorry for the one who bought your flat.
As I said before, it is better to let other have a taste of
their own medicine, if he play music loud, buy a powerful
amplifer with full concert speaker, blast them off, if next door
play basketball, you volleyball or soccer to make more noise, if
next door talk loud and alway quarrel, you can also talk louder,
open house party all nite,...these are the ways to stop people,
police and complain is not going to much.
I dun think this will work....if you made more noise, u become
the inconsiderate neighbour liao....