Loud clunk when humidifier turns off

Recently I had a humidifier repaired, it needed a new solenoid. The humidifier never worked since we moved in but now that it is working, anytime it shuts off there is a loud clunk that can be heard around the house.

When I stand in front of the humidifier it doesnt sound as loud as I would have expected, seems like its coming from inside the pipes? Not sure how to describe it


Is this normal or is there something I can do or adjust?

oops.. 'now that its working'

sorry

You may need to add a water hammer arrestor in-line. Solonoid valves open and close quickly. Opening isn't usually an issue, but closing can be - water has inertia...and it wants to keep moving. It will have to stop quickly when the valve closes, and this can cause things to move.

A hammer arrestor has a piston and a sealed air chamber or an air bladder (depends on the type). It needs to be installed close to the offending valve. But, it will be a long-term solution that should fix the problem. Sioux City, Watts, and others make them. They aren't particularly expensive ($10 or so), and should solve your problem, but they do require installation.