These people:
https://www.soundstop.co.uk/soundproofing_walls.php
have some web pages describing various options.
Is this an internal wall, or a party wall? What sort of noise is the priblem?
Just general noise from a bathroom, the wife doesnt want to hear what people are doing on the big white telephone......What sort of noise?
Big problem will be if the floor boarding (or joists if you're unlucky) run under the stud wall between bathroom & bedroom. You'll also be on a hiding to nothing if the loo is fixed to your common wall.
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