Its likely the water heater/element is scaled up that’s why the water isn’t heating up and is most likely what the popping noise is. You can try replacing the element first if still a problem replace the water heater.
If you feel popping noise from water heater, consult a plumbing contractor regarding replacement of the anode rod in the tank. Anode rods are specially designed to attract minerals and can deteriorate over time because the popping noise is the result of mineral deposits in the tank. An ineffective anode rod helps to build-up of minerals, leading to popping noises and other problems. Hope it would be cooperative for you.