We use to have that problem on our old rig. Many rigs have a mixer valve. It too builds up with calcium and starts to moan, squeal, so to speak. You might notice a decrease in water pressure too. It mixes the hot and cold water ( thru hot water line). It allows the hot water tank to heat hotter and not burn you by mixing with cold as you turn on a faucet.
Three times we replaced this in just over 5 years. Note item below might not be for your rig
https://www.amazon.com/Atwood-90029-Mixing-Valve-Heater/dp/B00HTN4PXE