The answer to 'water heater making noise' is that a noisy water heater is often caused by sediment buildup or mineral deposits inside the tank. This can lead to rumbling, popping, or banging sounds as the water heats up and the sediment shifts. Other potential causes include a failing heating element, loose parts, or a problem with the pressure relief valve.
If the noise is mild and intermittent, you may be able to address it through simple maintenance like flushing the tank or draining a portion of the water. However, if the noise is persistent or accompanied by other issues like leaks or reduced hot water output, it's best to call in a professional HVAC technician to diagnose and repair the problem.