I have a H250FDN and when ignited it has a low frequency jet engine like rumble. I have done some research and all I can find are articles relating to clunking and banging noises due to a broken bypass. I don't believe this to be the case as the only sound is a low "jet engine" like rumble. I have tried adjusting the gas pressure setting on the regulator (1 turn counter clock wise) but did not notice a difference and did not want to go any further.