A noisy water heater is often caused by sediment buildup at the bottom of the tank. As the heating element warms the water, the sediment traps moisture, creating popping or rumbling sounds. Other causes include a failing heating element, high water pressure, or fluctuating water flow. Regularly flushing the tank can help remove sediment and reduce noise. If the problem persists, it’s advisable to have a professional inspect the unit to diagnose and fix any underlying issues.