Can anyone tell me why the chips keep catching on fire in my MES40. I get the unit up to temp, load the chip sleeve with chips and within about 5 minutes they start burning. Sometimes I'll even hear a "pop". But after a few minutes things seem to calm down and the chips start to smolder like they are supposed to. I've made sure the tray the ships fall into is fully closed so it shouldn't be getting a lot of air. Any ideas what I am doing wrong. Would I be better off using pellets? Any help is appreciated.