TL;DR: Most water heater noises come down to one of three things: sediment buildup, pressure trouble, or a part that's failing. Popping and rumbling usually mean it's time for a flush, and you can handle that yourself. Hissing near the pressure relief valve is the one sound that means stop...
Extend Your Water Heater’s Life: Flush the Sediment
That rumbling sound coming from your water heater isn't your imagination. Sediment builds up at the bottom of the tank over time, and it's one of the most common reasons water heaters lose efficiency and fail early. Most homeowners don't realize their tank needs this basic maintenance until something goes...