I was cleaning one of my vacation rentals. I turned on the MOEN shower
water control. In the middle range, where the warm water would be, there
came a pulsing sound that sounded very regular and harmonic. If you turned
it to hotter or colder, it went away, but if you approached middle again, it
would start, and make an audible sound whoomp whoomp whoomp. The water also
varied in strength, and spurted slightly with the harmonic waves.

Any ideas of what is causing this or how to cure it? Install water hammers?

Steve