I'm running the stove pretty solidly now, 4f outside, 85 in the stove room. I'm getting a reasonably consistent thump out of it, maybe every 4-5 minutes or so. It's a deep sound, it almost sounded like a car door outside. I can't narrow it down to feeding cycles or anything. I just cleaned within the last 2 weeks, everything looked good. Is there any chain drive I should be looking at? Any other suggestions?