We just installed a water efficient (1.5gpm) shower head in our shower. About a week after we installed the shower head, we now experience the pipes behind the shower wall humming loudly while the shower is on (oddly enough, not when you turn the shower on, but a minute or two afterwards, until you shut the water off). When this humming is happening, the pressure of the water is reduced as well (and sometimes the humming will reduce to a low whine, but the shower pressure never returns). You can feel the vibration in the shower control knob. The humming stops when the shower is turned off. Any ideas on what we should check out?

Humming and noise= vibration.
Something's loose some where.
Let's find out where.
First remove the new shower head and turn on the shower. Still humming at you? Let me know, Tom

Thanks for responding! I removed the new shower head (it is a High Sierra adjustable showerhead) and the humming did not occur. I put the HS shower head back on, and within a minute of turning on the shower, the humming started.

Check the shower head for anything loose. It you can't locate anything take it back as defective. Good luck, tom