Gang, An issue has come up that has me a bit frustrated. Another poster had a similar problem, but that thread did not lead to a solution. Setup: -P61A -Vented with 4ft rise of straight 3-inch pellet pipe, 45 elbow, 2 ft straight 3 inch piece, and then an adapter takes it to stainless 4 inch flex liner up another 12 feet -Outside air kit -Stove is kept cleaner than Felix Unger would. I actually do a Harman "once a year" cleaning once a month. Problem is that 75% of the time, the flame flickers/flutters heavily, and the stove resonates like a washing machine that is out of balance. Problem is completely aleviated by opening the hopper lid, as the resonating stops and the flame goes from lazy yellow flickering to blue/purple blowtorch. I took the thing completley apart yesterday, including removing the outside air kit, removing the air intake port and sweeping the intake, cleaning the ESP probe, sweeping the vent system, removing fines from the collection site, cleaning the vaccum hose with a pipe cleaner, cleaning out under the burn pot, cleaning motor fins, etc etc etc. No obstructions in the outside air line or internal air intake path were found. Dang thing just seems like it's choking, and my dealer (who is completely clueless) does not know why. He said he called Harman, and they said my issue was completely normal. Not trusting this, I called another dealer who talked to Harman, and the Harman tech said there is definately something wrong with the stove, probably an obstruction in the air intake line. I adjusted the draft screw, nothing, checked to make sure the burn pot air holes were clean, and nothing is found. I know this stove operates on a negative pressure to prevent a hopper fire, but this seems way out of balance. Any ideas would be greatly appreciated, thanks.