DIAGNOSIS Accumulated grease behind the rear fan guard and heating elements is common. It can smoke during preheat and is a fire hazard if left unaddressed.
FIX The unit must be completely cool. Remove both baskets and the crisper plates. Wipe the main cavity with a damp cloth. For the rear section: Use a long-handled, soft-bristled brush (like a grill brush) to gently dislodge debris from the heating elements and fan guard. Do not use metal scrapers or excessive water. A vacuum with a crevice tool can then remove the loosened particles.
IF THAT DIDN'T WORK For stubborn, baked-on grease, create a paste of baking soda and a few drops of water. Apply it sparingly with a cloth to the greasy areas on the metal interior walls (not the elements). Let it sit for 15 minutes, then wipe away. The mild abrasive will cut the grease without harsh chemicals.
HEADS UP Never immerse the base unit in water or hold it under a running tap. The heating elements and electronics are not sealed. Liquid ingress will cause permanent damage and an electrical hazard.