Just converted a wood burning fireplace to a natural gas one and there is a jet engine sound when opening the valve and lighting the burner. We tied into my existing 2" line coming into the house with 1/2" pipe. There is about 5' of 1/2 inch pipe from where we tied in to the burner. It is not the whistling sound some describe as being associated with flex pipe. There is a 12" piece of flex from the control valve to the burner. After adding a regulator which is set at 3.5"WC we had the local gas company check and confirm pressure from the meter is 7"WC and the meter is operating as it should. The regulator seemed to reduce the noise slightly but did not eliminate. The only time you do not hear the noise is when the valve is open fully...anything less and you can hear it. Removed the burner and lit just the end of the flex pipe and you still hear the noise. Two plumbers later and a visit from the gas company and no one knows. Any ideas of what might be causing the noise?