I have an interior wall that separates a bath and a bedroom. When the shower is used, it is very noisey. Noise is most intense from behind the shower head in the wall . It is a very common water pressure sound. How can I insulate this noise from the bedroom, since I currently have the wall opened up, and the plumbing exposed?

I would do two things. First, I'd try another shower head to see if a different design has less water turbulance. Save your receipt and take it back if it does not help. Your can fill the awll cavity with unfaced fiberglas unsulation. Don't pack it tight, fluff not stuff. Do not use expanding spray foam in this application.

I have an interior wall that separates a bath and a bedroom. When the shower is used, it is very noisey. Noise is most intense from behind the shower head in the wall . It is a very common water pressure sound. How can I insulate this noise from the bedroom, since I currently have the wall opened up, and the plumbing exposed?
Your shower arm's secured by a drop eared ell,(see image) that's screwed to backing. If the screws are loose then that would give you the problem that you have. Also checl the pipe strap on the shower raiser and the straps
Securing the shower valve. Good luck, Tom