Most of the time a water heater makes a rumbling noise because it has a large build up of slush at the bottom of the tank. All water heaters have an Anode Rod. This rod is made up of zinc composites (normally) and its purpose is to react with the bad minerals in the water and neutralize them. In doing so it flakes off the neutralized minerals. These accumulate at the bottom of the tank. In this area (the Salinas Valley) the water is extremely bad and these anode rods get eaten away very quickly, which means that that slush develops quickly. The water alone in this area has minerals that develop at the bottom of the tank along with the anode rod flakes. That slush at the bottom of the tank acts as an insulating blanket. The heat sensor to tell the heat (flame or electricity) to shut off is located at the top of the water heater. Therefore, the blanket at the bottom of the tank is keeping the heat from getting to the sensor at the top. The water heater works extra hard to get the heat to the top of the water heater and it eventually starts to boil and that chunky slush gets pushed all over the tank. This causes those “pops” and “gargles”. Water Heater In order to fix this problem you should flush your water heater by first turning the gas valve to the pilot position. Then you should hook a hose up to the hose bib on the water heater. Next you should turn off the cold water valve going into the water heater. Open the hose bib and drain to the street. After the tank is drained leave the hose bib in the open position and turn on the cold water valve to flush the unit. When done, and the tank is full, turn the gas valve back to the on position. For additional help please e-mail.