When we turn on our hot water, it makes a loud hum. It also hums from the oil heater, through the pipe and to the faucet we have on. Its gotten a lot louder over the past couple of weeks. There is no noise when the water is off. The noise is a low sounding hum, not like a squeal... (do, ra, me , fa , so, la, te, do)... its on a scale of (so)... Please if anyone can help me fix this issue??