: I recently bought a home with a 10-year-old State brand 75 gal. water heater. Whenever it runs, it bangs quite loudly. In fact, it sounds like someone knocking on the door, and you can hear it from the opposite end of the house. What causes this, and is it dangerous? The first time I heard it it really scared me. Thanks.hello ,usually banging water heater are result of build up of calcium in the water heater when the heater fires they explod internally, try flushing water heater out first ,see if that help , and if it is a electric heater also replace the heating elements , roger ryals