I recently, 6 weeks ago had installed a chimney with my Hearthstone stove. The stove runs 24/7 and we mostly run elm. In the last few days I've heard what sounds like something fall down the chimney, everything is still attached up top. I run flue temps of 400-600 measured with a probe about 30" above stove. I think this is creosote falling off the interior of the chimneys wall but thought I would ask the professionals.