Water hammer-Clunk

I have a toilet in the Master bath that has a clunk(pipe rattle) after the tank is full and shuts off . It has a flowmaster 400a and I cleaned it to be sure there was no restriction. The inlet valve is open all the way. If I partially close the inlet there is no clunk but there is water hammering. The toilet 19 years old.
Will I have to cut a hole in the wall behind the inlet pipe and secure the pipe better? Or do I need to replace the inlet valve?
Any advise would be appreciated. Thanks in advance

I have had the same problem and found the fix to be replacing the fluidmaster value in the tank with a Korky value fix the problem. They do not cause water hammer.

clunk

Start by chainging the ballcock......

clunk

Go to HD and buy a Fluidmaster replacement cap and snap it on in place of your old one. But first observe your Fluidmaster when the clunk occurs. If the upper portion "jumps up" when it clunks then you need a new valve.

You can repair the Fluidmaster, but if you want less hammer, put in the Korky Quietfill.