Why does my shower fixture groan every 10 seconds?

Question

For a few years now I have noticed a groaning noise from the wall behind my bedroom shower valve every time a water faucet is turned on and off anywhere in the house. Today I noticed that groaning noise happening every 10 seconds regardless of what's happening with any other water fixture. It stops when I close the inlet valve to my water heater. My water heater is a relatively new 50 gallon Rheem.

I put a pressure valve on my garage faucet and turned only the hot water on. The pressure ticks up about 1 psi in the same intervals as the groaning noise. I also did this for the cold water side and it's doing the same thing.

So apparently the groaning is only associated with the hot water side of the shower valve. But the water pressure fluctuations seem to be happening throughout the entire water system.

This is a four unit town home with one water meter for the entire building.

I guess I have two questions:

1. What might be causing the groaning sound in the wall behind my shower valve?
2. What might be causing the pressure fluctuation and is it a concern?

Answer 1

This is a common sort of issue with a tap that has an "anti-scald" function built in, (as virtually all modern showers do) and can cause a variety of odd issues, such as cold taps running hot because the anti-scald is malfunctioning in such a way that it passes hot to cold. The "anti-scald" mixes cold with hot to prevent the hot from being too hot when working correctly. When working incorrectly it may pass water in either direction.

The thermo-regulation function of such taps is before the water delivery part, and can activate inappropriately without the associated tap/shower being on.

Thus, the groaning and pressure fluctuation would both be caused by your shower valve anti-scald valve inappropriately activating and passing water from hot to cold or cold to hot.

If you have a shutoff for the shower supply, you can try shutting it off (as you did at the water heater already). Presumably shutting off either the hot or the cold (or both) to just the shower would stop it.

Presumably a "cartridge replacement" (theoretically easy, often not that easy since things get stuck with decades of use) or entire valve replacement (far more complicated and generally involving opening the walls) would address it.