I am new to pellet stoves and just purchased a Cab 50 and installed in my basement. The stove seems to work fine however 2 days ago at times it rumbles like a freight train every once and a while. I spoke to the dealer and he suggested i close the feed door down a little, didn't seem to help.My venting is vertical for 4' then horizontal for 1' through wall to termination cap. Any ideas? Rick