Hot water tank on gas made high pitch noise

[LovingIt]

Hi guys, along with our never ending long list of non-stop issues (which I have yet to share the misery) with our 2019 375res Solitude lemon, we picked up the trailer may 3 and moved into it fulltime late July of this year, so dropping off the trailer at the dealers is not an option. Anyway we had a weird thing happen late last night, our hot water tank has been on gas while we are hooked up to 30 amp so we can run other appliances. It has been on gas off and on between electrical at night this past month with no issues with it ever till now. When i went to the bedroom is when i heard this high pitched sound, so I don’t know exactly when it started as you cant hear it in the living room (other end of the trailer) we turned the hot water tank off and onto electrical and it stops, wait a minute and back on gas give it a minute, we here it light and again back to the high pitch sound. It’s like 2am when this was discovered (watching a late night movie) so didn't take the hotwater tank outside panel off to trouble shoot, its pitch black outside, we figure we’ll wait till morning light. Morning comes and we turn it back onto gas from electrical and no sound! (Yettttttttttt.) I’m reaching out because we never experienced this with our other two trailers from the past, and we have the dealer working at a snails pace on all the other list of issues, thus i’m trying to be prepared as we leave to Osoyoos dec1 for xmas from Surrey bc, and our fridge is a problem still and yet to even be looked at, that i think i’ll blow a gasket if the hotwater tank goes so I’m hoping someone knows what caused the sound. Its a suburban 12 gal hotwater tank. We were not able to know if it was heating because we did not run the hot water to see if it was hot, too stupid that late at night didn’t think of it.
So just based on high pitch noise when on gas anybody know what caused it? The noise almost sounds like a neighbour running their vacuum, you know that high pitch noise. (Nobody beside us, let alone running a vac at 2am, that stops n starts with our hotwater tank switch, and i have a better chance of winning the loto than that being a coincidence, lol).

[FT4NOW]

Could be the relief valve chattering. You say the noise stopped on electric mode. Are you sure the heater was actually on? Some water heaters have 2 switches to turn on electric, one inside the RV and one on the heater itself, both need to be on. If you only turned on the inside switch, the heater wasn't actually on electric mode. I've heard of this noise happening due to relief valve chatter or water boiling around the heating element and reverberating the sound through the tank. The fix for the sound issue is to shim the tank a little bit and it goes away.

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[powerscol]

Did you happen to just change LP tanks? I had my water heater 0n my old unit (same brand as yours) sound just like that and all it was is the gas orifice/air mixture. It will blow hard making the sound until the LP settles down (air bleeds out). The flame color should be blue - if yellow the air mix is out of wack. Bugs love propane so check the fittings for cob webs, etc.

Hope this helps

[LovingIt]

Yup, heater was on via both switches inside n out. Nop did not change tanks. Nop, no bugs/spiders/ webs.
Weird thing has not repeated itself, so it must have been something like the propane air/mixture. Bit of a relief.
Thanks guys for the possibilities of the cause. Cheers!

[boyscout]

Yup, heater was on via both switches inside n out. Nop did not change tanks. Nop, no bugs/spiders/ webs. Weird thing has not repeated itself, so it must have been something like the propane air/mixture. Bit of a relief. Thanks guys for the possibilities of the cause. Cheers!

Glad that it's gone. Maybe you were nearing the end of one propane tank and then the regulator auto-switched to the other tank? If it recurs try closing both tanks and then opening both slowly, opening the currently-active one first.