One of our tenants in a single-family home complained of a hammering sound when she turns on the shower. (She sent us a video which I tried to attach, but the file was not accepted. We have not directly observed the problem ourselves.) When she first turns the shower on, the hammering sound is continuous and rapid, and the water pulses in rhythm with the sound. When she adjusts the valve, it goes away, and when she returns the valve to the same position it had when the hammering started, the hammering sound does not return.
Also, the shower has a single valve.
This sound has been there for at least 15 months, since they moved in, but they just now let us know.
Any ideas about how to fix it? Just lower the water pressure, or is something else probably the cause?