bathroom shower making noise when water turned off

[skm1001]

Hello
Our bathroom shower is making some sort of weird noise when water turned off, as if it is taking some air inside.
Following is the report from the house inspector:
When I turned off the bathtub water while it was in the shower mode, there was a good deal of water hammer. When I turned off the bathtub water while it was in the bath mode, there was not. Have a plumber evaluate and repair the water hammer prior to the end of the inspection period.

Thanks in advance for your help.

 

[frodo]

If you have a loose pipe in the wall at the shower
it will move when another faucet turns on

if it is an upstairs shower, peg the holes where the water comes up thru the floor

 

[Geofd]

I have experienced the packi g nut u def the handle being loose allowing the graphite packing ring to move around causing symptoms like this