Water heater noise

[Sinterior]

The water heater has started making a low pitched hiss when heating on electric, and I don't know about propane as it may cover up the sound.
It does this whether running the hot water or not and stops when the water reaches its temp.
I've purged the tank with the relief valve and no air came out.

Thanks in advance for any help or suggestions.

Peter

[PapaBeav]

Ours will make somewhat of a hissing sound when it is first turned on when on electric. But that is just the cold water on the electric element as it is heating up. I only hear it if I am standing near the tank outside, never inside. And only when it is heating. Not sure if that is what you are talking about, but hope this helps.

[racerjoe]

Ours does the same thing on electric,but water is still as hot as when on gas and have not had any problems thus far.

[illapah]

Noise my be caused by mineral buildup on heating element. Same for the temp decrease.

[ole dude]

Its just the electric htg element cooking the H2O.

[Sinterior]

Thanks all, now DW can relax and not worry.

[randye]

Heavy minerals in the tank can trap air and sometimes release and will make the noise. Some have found the check valve in the tank itself has a piece of meneral stuck in it or is broken. If it goes away soon, I wouldn't worry. Have a good Sping and Summer.

[farmboy]

I have heard the same noise when I have serviced or installed a new home heater and the water is cold. When I hear that sound I know It is working .