The answer
Popping/rumbling ("kettling") is caused by calcium carbonate sediment buildup at tank bottom; boiling water trapped under sediment pops through. Insufficient hot water occurs because sediment insulates heat transfer, electric elements/thermostats fail, or a cracked dip tube dumps cold incoming water directly at the hot outlet. Flush tank annually; inspect sacrificial anode rod every 3-5 years.
Sources
This answer is drawn from the standards and guidance below. It is general information about how these systems work — not a diagnosis of your property.