can someone help? My gas GE 50 gal water heater has a low hum after about 1 min after running. this unit has air inlet vents on the side and this is where the noise is coming from. I have flushed the tank 2 times did not help, I can blow into the vents and the hum goes away. the flame is blue and the gas line does not vibrate.? what would be causing this hum? the water heater is only about a week old.