Why is my water heater making a popping or rumbling noise?

That noise is almost always sediment — mineral deposits from hard water that have settled on the bottom of the tank. As the burner heats the water, it has to work through the sediment layer, causing the popping and rumbling sound.

Beyond being annoying, sediment reduces efficiency and accelerates tank failure. Flushing the tank annually prevents this buildup.

If you're already hearing significant noise, it may be past the point where flushing helps — have it evaluated before it fails unexpectedly.