If the shower valve is noisy when the shower is in use, and your incoming pressure exceeds 5 bar, please ensure you have fitted a pressure reducing valve in the mains supply pipe, immediately after the stopcock to the premises.
Several different noises can issue from a shower valve that isn't working as it should be.
Whistling sounds - this is likely the symptom of a worn gasket or washer as they become thin enough to vibrate as water flows past causing a whistling noise. You will need to isolate the water supply, disassemble the valve and replace the rubber seals. If the whistling continues you may need to replace the valve itself.
Rattles and Thumps - this is normally from the pipework behind a shower and is usually because they have not been secured insufficiently to the framework or have just worked loose over time. You will need to secure the pipes, if you can't get access to them from a panel or adjoining room and can't put up with the noise you may need to create a new access.
Knocking - A loud knock when you turn on the valve, or when the valve is set at a certain temperature may be caused by 'water hammer'. The high pressure causes the water to hit against the inlet valve as it is opened and closed. You can usually adjust the water pressure to the shower by lowering the amount of water going to the shower and therefore reducing the noise.