Various things you can try

Examine the structure of the party wall to see if there's a cavity you can fill with foam

Build a false internal wall, filling the gap with thermal insulation. (I am told by the architect IC Operations at Git Towers that the sheepswool insulation is pretty good with noise.) There are more sophisticated versions of this eg User Posted Link

Apply acoustic panels (not as good as the false wall but cheaper and consumes less of your room).

Be warned though - as TAICOGT is always telling me, sound will always try to find a route

Posted By: Old Git, Apr 20, 13:50:11