I've recently openned my water heater drain several times to flush out sediments. Once I did see a white sediment come out. However, inspite of repeated flushings, my heater still rumbles when the water is heating. It didn't do this when it was new, and it's only about two years old. Is there a better way to flush the sediments, besides just opening the drain valve? The heater is near my bedroom and the rumblink is annoying.