Hello. This is my first year of burning and I was outside moving snow today, looked up at my flue and noticed some brown gunk on the side of it. I attached some pics for you all to see. What is this? I stopped burning for now until I figure out what the problem is. Is it creosote? The main pipe in my living room sounds hollow when I tap it so I guess that means is empty? I have attacked pics of the stove in my living room. There is only about 6 feet of stove pipe coming out the roof