I assume this is normal, but wanted to check with others. When the temperature starts to warm up in the smoker, I am getting a lot of smoke, and it appears to be a dark gray. After about 15 minutes, the smoke comes out in puffs, and then it seems like the unit exhales deeply and the smoke comes out from all around the door. After that, all is well and the smoking process works fine. Is this normal to have a kind of implosion that blows smoke all around the door seal?