My wife became concerned with a noise she heard from our water heater today and unfortunately, I am not an expert home repair man. Our water heater normally pops and bangs when hot water is used, as we expect it would. But it is also now making a "whirring" sound near the base and neither of us have noticed it before (not to say it hasn't made this noise before, just that we haven't noticed it until now). It sounds to me like perhaps the gas is heating the water?? My concern is that it doesn't stop -- this is a constant sound. Can anyone tell me what this is/could be? Thanks!