Hi Chloe, start by isolating the source :) Run at 400°F with the basket seated but without the crisper tray or racks; if the rattle stops the tray is vibrating and slightly bend or temporarily shim its tabs with folded foil to confirm. If it persists press gently on the top and side panels with an oven mitt while it runs; a change points to panel resonance or loose feet, tighten exterior screws, make sure all feet are present, level the unit, and test on a heavy cutting board to decouple the counter. If it still rattles preheat until the noise starts, then cancel and unplug and listen to the fan spin down; scraping or ticking on spin down points to a loose or warped fan or shroud. When fully cool remove the basket, look up at the fan and element area for rub marks or debris, check that the fan nut is snug, and spin the fan by hand to feel for wobble. Tap the element shield and nearby brackets when cool; if they buzz, snug their screws. If nothing changes and the noise only appears at high heat the motor bearing or fan assembly is likely defective; document the symptom and use the warranty.
