That sort of noise is usually caused by water pressure, if you can reduce the flow rate by closing the isolating valve slightly on the cold supply first, as this is probably mains pressure which will reduce the flow rate and the pressure to the shower head. It is a bit of a trial, if it works great, if it doesn't you can always put it back to where it was and try the other isolating valve but it is usually the cold supply that causes this type of problem. Hope that helps.
Brian,, October 2012
