New water heater "moaning"
Recently installed an A.O. Smith 50 gal. gas w/h. When the hot water is first run at any faucet or shower in the house, a humming moaning sound, like a fog horn in the distance, comes for a just few seconds, goes away, and then several seconds later a second slightly lower pitch sort of echos the first, then goes away. This only happens rigt when hot is used after not being used for a while. Not super annoying, but concerning that something may be wrong. Hooked up exactly to same existing waterlines and gas lines as the non moaning heater it replaced.