If your water heater is struggling here, the hardness of the water is the first thing worth ruling out.
Scale is usually behind it
Minerals settle in the bottom of the tank and bake onto the element or burner. That is what causes the popping and rumbling, and it is why heaters in this area often do not last as long as the label promises. If an element has been replaced once already and failed again, sediment is nearly always the reason rather than a faulty part.
What is worth repairing
A thermostat, element, thermocouple or gas valve on a tank under about eight years old is normally worth fixing, and flushing the sediment out often makes a genuine difference to how it performs.
What is not
If the tank itself is leaking rather than a fitting, it has rusted through and no repair will hold. We will tell you that plainly rather than take payment for something that will not last.
Worth doing while we are there
Flushing the tank, checking the anode rod and testing the pressure relief valve. In water this hard those three things make a real difference to how many years you get.