Is it the steel expanding and contracting that makes the noise when the fire is going? I get the steady tic, tic ,tic in the stove pipe as I heat things up or damper back down and a deeper tunk, tunk or thump, thump in the stove when it is heating up. You can actually feel the stove tunks if you are standing next to it. I am burning a VC Defiant. Does anyone know what is actually happening other than "expand/contraction of steel" - or is that just it?