From the Sioux Chief page
"Water hammer is usually recognized by a banging or thumping in water lines when valves are shut off. Although this is an easy way to recognize the problem, water hammer doesn't always make these tell-tale noises.

Water hammer occurs when the flow of moving water is suddenly stopped by a closing valve. This sudden stop results in a tremendous spike of pressure behind the valve which acts like a tiny explosion inside the pipe. This pressure spike reverberates throughout the plumbing system, rattling and shaking pipes, until it is absorbed.

Normally, a sufficient pocket of air will absorb such a pressure spike, but if no pocket of air is present, expensive fixtures and appliances within the plumbing system will be damaged as they are left to absorb this pressure spike. "
Sioux Chief

Steve,
You may want to install a shock arrestor before the shutoff to give a place for the spike to go. I would size it for the 1-1/4" line you are using. This may be a simple fix for the problem that you have.

• Water Hammer Information