DIAGNOSIS Something is interfering with the fan blade. It's either a piece of loose food/debris caught in there, or the fan blade itself has become unbalanced or loose on its shaft.
FIX 1) Unplug and cool. 2) Remove the basket and pot. 3) Look into the main chamber and use a flashlight to inspect the fan blade near the heating element. Use long tweezers or needle-nose pliers to carefully remove any visible debris. 4) Gently try to wiggle the fan blade—it should not move side-to-side.
IF THAT DIDN'T WORK If the noise persists and the blade seems loose, or if you see no debris, the fan motor assembly is likely faulty. This is a repair for Cosori technicians.
HEADS UP Always let large crumbs fall into the basket, not the main unit. Avoid shaking the basket directly over the heating element chamber.