. Here's a fun one. It didn't happen when I was at his house, but fortunately he made a video.

. Banging of pipes at unpredictable times. Water is NOT being used when then banging occurs. As you'll see in the video, when the inlet valve to the water heater is shut, the banging stops.

What I noticed
  • A VERY slight bang when hot water in kitchen was turned on and off. We were trying to imitate the problem, though this may have nothing to do with it.
  • A VERY slight sizzling sound like a hamburger on a griddle, only fainter, when I turned the water heater on. Perhaps that is normal.
  • A VERY slight tapping with the same or similar rhythm shortly after the water heater was turned off. I didn't wait around forever so I don't know if it would have gotten louder.

What I know
  • It is a Ruud electric heater PE2M-52-2
  • Water pressure in town is high, 80psi or more.
  • He does not have a pressure reducer. Almost every house in town does.
  • This has not been going on forever, only the last few months.

What I checked
  • Drained heater to check for sediment. Some in first 5 gallons, but not much.
  • Dip tube is intact and the bottom, at least, looks fine.
  • Elements seem fine. Only slightly corroded.

My theories which I don't have much faith in.
  • Air in top of heater? Shouldn't it work its way out?
  • Change in water pressure that a pressure reducer would solve? One that handles thermal expansion also? Then again, if it really is happening after the heat is turned off, I guess that's thermal contraction.
  • Add a water hammer arrestor? But where is it happening, and why now?

. Thanks for your thoughts. I'm hoping he will come up with a few more clues, as now he can audibly tell when the water heater is on.