Diaphragm and Regulator
One common cause of humming in gas grills is the vibration of the rubber diaphragm inside the regulator. When temperature, atmospheric pressure or humidity changes, the diaphragm can vibrate – making a humming sound. The sound will subside when atmospheric conditions change. High gas flow can also cause the diaphragm to vibrate. You can try reducing the flow – this will change the pressure inside the regulator and may cause the sound to stop.
Another source of humming or fluttering noises is the grill. If the slide-out portion of the bottom tray is not pushed completely back into place after cleaning, excess air may be drawn into the grill. This air then expands and can make cause the tray to vibrate, leading to a humming or fluttering noise. When the lid is opened, air may be drawn into the grill, also potentially causing a humming or fluttering.
Air in the Line
Air trapped in the line leading from the fuel tank to the grill can also be a source of humming noises. Air in this line can vibrate, similarly to air in a flute, causing humming. The air may vibrate due to changes in temperature or pressure and can become quite loud. This can be fixed by purging air from the line according to the manufacturers instructions. A lower humming or rushing sound may be caused by the sound of gas flowing in the line. This is normal and fairly common in gas grills and can be ignored.
When to Worry
In most cases, humming noises are a perfectly normal part of your gas grill operation. If you smell gas or hear a whooshing sound of gas escaping, in addition to the humming noise, this can signal a gas leak. In this case, you need to disconnect the hose from the tank and move the tank away from your house. You can then call the manufacturer for advice and assistance. Humming may also be caused by a faulty regulator. If you suspect this, for example if your regulator is not holding pressure, then it should be replaced as it can leak gas.