Help needed - Atwood 10 gal Water Heater - Noise at Relay?

[BeHappy]

Couple days ago, dry camping, and turned on pump. Heard usual pump motor noise -- but this time it was accompanied by a scratchy-buzzing sound?

(After reading on other threads this forum of water damage when pumps left on if a line breaks, etc - we no longer leave the water pump turned on. Instead, we turn on / off as needed for each water use. )

We tracked down what we think is the source of scratchy noise - seems to be coming from Hot Water Heater tank 'relay switch'? Looked up in our WBG manual, (black cover box about 4" square, located on rear of W/H, as seen from inside coach, under rear lavatory in our 2013 Journey 36M).

We have a 10 gal Elect / LP Atwood Water Heater in this coach.

First, what does the relay switch do? Was surprised that even though no LP or Elect turned on at W/H control on 'One Place' panel, no hot water demand at faucet ...why there would be anything to do with water heater -- since only switch we turned on was 'water pump ON.'

Second, more important I guess ... what to do to fix / resolve this noise?

Thanks for any help /advice in advance.

Safe Travels to All

[YC1]

Without a picture it is a guess but it may be a 12 volt controlled relay that switches the 110 volts on and off to the water heater. Check your HWH 110 volt control switch. Move it to the other position and check for noise. Do not rely on seeing a light on or off at the panel. Lights burn out.

[DancinCampers]

If the noise occurs while pump is running, it may be the check valve on water heater.

[mjeffrey]

110 volt line goes all the way to rear of water heater even when electric side turned off. Relay (yellow line) lets ac thru to heater element when electric side enabled and water temp is below threshold. If water is leaking in that area, watch out! Turn off ac at breaker panel to truely eliminate 110 involvement.

Scratchy-buzzy sounds like it could be electrical, but don't see how pump switch would effect this.

Turn off water heater breaker and repeat to see if anything changes.

[Doug Sage]

I had the same issue with my 10 gallon Atwood. It was the anti-siphon valve on the back of the water heater. I replaced the valve to solve the problem.