Water heaters typically are popping due to the minerals in hard water which settle together at the bottom of your water heater over time. The minerals make that popping noise when they hit the side of the tank. It is completely normal to have this build up over time if you do not use a water softener. Although this is very normal, it is something to keep an ear open for. If your heater is popping louder than a coffee maker sputtering, you may want to follow these steps to flush your water heater tank of the remaining sediment.