What youve described , is, condensation that forms when you run the water heater under high demand (cool water inside the tank being heated) =A0=A0This makes more of a 'sisssssssss- ing ' sound than a pop ; if the popping noise occurs ALL the time the water heater is firing (even during a normal cycle of low demand...), then, its sediment in the tank instead of condensation on the outside of the tank. As a safety precaution, id replace a gas water heater at 15 years maximum ..and less , if its located in an area that will cause major damage when it eventually leaks.. 'This is Turtle. Yes I can see your point there about the sissssssssss- ing sound than a pop noise. Cold water boils faster than hot water and will make a boiling noise when heating up. Now you need to send this endless void of Knownledge to all the hot water tank companys for them to try to stop this condition. I do you suggest about getting rebate on your next hot water tank change out for suppling them with this endless void of knownledge. TURTLE '
ME: The water heater manufacturers are already familiar with condensation occuring during high demand because they put it in their owners manual that ships with the tank. The knowledge i imparted was for the benefit of the OP which is what a NG is for. How about if you and I have a truce Turtle ? Shall we work toward this end ? Im willing.