My electric water heater started to make a noticeably louder hissing noise periodically. It used to be a low level hissing noise. I am assuming this hissing is when the thermostat is turning on the heating elements to heat the water. About 6 months ago I removed the heater and reinstalled it in the same spot when I was renovating the area for a laundry room. I mistakenly connected power to the heater before it was filled with water and the upper heating element burnt. I replaced it and everything was seemingly ok till now. It is a GE and has a manufacture date of 2/2006. Is there a problem?
Sediment may have formed around the heating elements. Water within the sediment may sizzle and boil rather than commingle rapidly with the rest of the water. Few experts recommend draining the tank and taking out the elements every several years to scrape off the sediment and usually the sediment does not cause any harm except if it gets too thick the element can overheat inside and burn out. Sometimes the sediment will crack and fall off by itself as the elements turn on and off, expanding and contracting slightly. Sediment on the elements may also slow down the heating of a tankful of water.
When cleaning anything including baby diapers, it is better to sweep off or scrape off as much solid and semisolid material as you can first. (1) Less cleaning fluid or detergent needs to be used, (2) Less of a mushy mess which in turn means that bleaches or disinfectants will be more effective.