Been chasing an annoying issue with my Harman XXV (born in 2008). Once I get this handled, I'll be able to sit back and enjoy the heat... Stove continually sounds like a helicopter is flying over the house, but the frequency is about twice as fast. Flame flickers at the same frequency, almost acts like a strobe light... Very unsettling. â€¢ Well insulated finished basement install â€¢ Happened since day 1 â€¢ Selkirk DT Pipe (did it with Simpson too) â€¢ OAK â€¢ Up and out install - 5' up, then out â€¢ Round flame guide â€¢ Seems to happen at medium/high burn rates â€¢ Happens with all brands of pellets â€¢ Happens with or without OAK attached â€¢ Hopper gaskets seem well in place - I used aluminum tape on the inside joints of the hopper, no change â€¢ Door gasket and hopper lid gasket are fine â€¢ Vacuum pressure inside the stove is pretty high - .6" with the draft voltage adjustment as low as it will go â€¢ Restricting intake air helps, but don't want the flame to get lazy, currently 50% of air intake is covered, burned fine with 65% of intake covered (maybe a little lazy) â€¢ Intake flapper moves free, doesn't appear to be contributing to sound Drives my wife nuts and I'm not far behind... Please help me make this issue go away. Thanks in advance for your contribution!