I have a 17-year-old Rheem natural gas heater. According to our gas bill, we suddenly started using significantly more gas in September and October than the previous year. The only thing it could be is the water heater. Then today, I heard it making a quiet but noticeable sound. Imagine two (or more?) metal pieces gently rubbing together. It almost sounds like a wind chime rattling in the wind. Could it be done for?