Just got in from 18 days out and am wondering about the noise that my HW heater is making when using 120V.
It's nothing dramatic, but I can definitely hear it. Kind of a "chssssss."
My two previous trailers didn't make any noise when on electric that I can remember, but then again, maybe I wasn't around when they were heating.
Don't know how old your unit is,, but I would remove and check the Anode rod from the water heater. If it is in bad shape it can cause the heater to make noise. Something about electricity and water and the hardness of the water or something. I replace mine every year, only cost about $11--12. Make sure you relieve the pressure and your not plugged in when you remove it and also wash out the heater while your at it.
It is calcium and manganese hardness in the water you have been using. It is the same as the deposits left after hard water has evaporated.
The scale has built up around the element, so much so that water is not in direct contact with the element.
Turn it off, let it cool and drain the water heater. There is a flushing wand available to insert into the drain hole and flush out the heater. You can also insert clear plastic tubing and siphon out water and debris from the bottom of the heater.
2000 Sea Breeze F53 V10 - CR-V Toad
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If it's an Atwood water heater....no anode rod. Suburbans use them.
The area you were camping.....was water hard? Have you been where water was hard and used it a lot?
Mine made a strange sound (your description "chssssss"...very close). Drained/flushed/cleaned...got some debris out but still had sound. Finally accessed back/front (side where element was...inside under kitchen cabinet) and found very small leak (tiny, tiny dripper) when element turned on. Snugged up on element....no more sound.