Dometic 320 water valve

If the water pressure is good (you are using a pressure regulator)... not a Camco piece of junk.... then replace the valve

And if you let that foot pedal snap up hard you WILL sooner or later crack the pedal mechanism and be buying a new toilet...

I know they say to push down and pull foot away to let it snap closed. Try quickly lifting the door pedal instead. I have the same toilet and that is what I do in the middle of the night to make less noise and it still functions fine.

I am bad, it is an Oatey Water Hammer ARRESTER.

Allworth wrote:
Probably "pressure regulator", but more interesting is which valve closes so fast that it causes water hammer??

From the post title I think it's the toilet.

The water pressure regulator is good, and the resistors are like one for a washing machine.

This is the valve.

Probably "pressure regulator", but more interesting is which valve closes so fast that it causes water hammer??

What do you mean, resistor? For the pump?

Google water hammer.

Install a small expansion tank.