My 8 year old electric water heater started to make a strange rattling noise a couple of weeks ago. The noise happens at random and lasts for only a few minutes. Short bursts of noise about a minute apart and stops after about 6 rattling bursts. The noise sounds like a loud groan. I heard this sound about 2 weeks ago for the first time and I've only heard it about 4 times since.We have plenty of hot, clean and soft water. My tank is a RHEEM 40 Gallon. Is my tank failing?
Groaning, rumbling, or other low-pitched noises from a hot water heater are typical symptoms of excessive sediment buildup in the heater; normally, flushing it via the bottom drain valve is recommended to clean out the sediment buildup. If not cleaned out, eventually the heater's lower element will burn out due to being buried in insulating sediment (calcium carbonate).
Electrical components generally don't make noise and if they do it's a high pitched whine. Considering the main parts of a water heater are probably: tank, solenoid valves, heating element and some control unit; I would suggest checking out the solenoids or pipes.
Solenoids are electro-magnets that open and close the line to fill the tank with water. If you have them.
Otherwise, maybe most likely, the pipes are shaking from water flow. You could try wrapping them to stop the vibration...
Let me know what you've tried or if you can tell where on the machine it's coming from.