This is my first season with my VC Merrimack insert. I am noticing that it frequently makes loud popping sounds after it has been going for a while (seems the term is called 'Oilcanning"). I think it happens more with the damper all the way down ( like when we go to bed). The stove seem plenty hot, been when it gets going, it pops loudly about every 10 seconds. It keeps me up at night until I go down and load it back up with wood or open the damper up when there is wood in it. Everyone Ive talked to seems to think this is unusual including people who have the same unit. Is this a defect? Should I be worried. Its not even that cold yet here in NY. Temps probably in the 30's. Any help would be greatly appreciated.