DIAGNOSIS The DEHYDRATE function uses the lowest fan speed. At this speed, an unbalanced fan blade or a small piece of food debris caught in the fan housing becomes audible as a rhythmic rattle or grind.
FIX Power off and unplug the unit. Inspect the rear fan intake and the interior heating element area for any visible foreign objects using a flashlight. Use a can of compressed air (held upright) to blast short bursts into the fan intake and the rear vents to dislodge debris. Tilt the unit forward to help particles fall out.
IF THAT DIDN'T WORK The noise may be from the fan motor shaft itself. While unlikely, if the noise persists across all functions and sounds metallic, the motor bearings may be failing. This requires contacting Ninja customer support for a repair assessment.
HEADS UP Do not attempt to remove the rear fan guard yourself. It is not user-serviceable. Tampering with it will void the warranty and can damage the fan blade balance.