Most water-heater noise comes from sediment that settles at the bottom of the tank. When the burner heats water trapped under that layer, it bubbles and pops.
A yearly flush removes most sediment. If the noise has already started, flushing can still help, but a tank that’s over 10 years old may be nearing the end of its life.
Call a technician if you hear loud banging, notice leaks, or see rusty water. A water softener can prevent sediment from building up in the first place.