there is a click when the piston moves but it shouldn’t be too loud. Running the valve at the wrong voltage can drive it harder and produce a louder click so it is worth while confirming the voltage you are using.
To dampen the piston you could try stretching out the spring a little, this would change the performance of the valve a little bit but not enough to make much difference. To stretch the spring you need to dismantle the valve.
If you need very quiet operation you may need to look at non-metal valves. There are several with plastic bodies such as the 2P025-08. Alternatively look at the all-in-one valves. These tend to be slowly though.
What are you using the valve for?