Hi. I've had my RT-590 for a few months now. I just started seeing a large amount of ash or dust residue on the grill after some cooks. This turkey cooked for 4+ hours, and I think the ash or dust is a lot more than should be. I vacuumed out the grill 2 weeks ago, and have done a few cooks since then. I'm using weber smokefire hickory pellets. Any ideas?