DIAGNOSIS A consistent, rhythmic ticking is usually the metal heating element expanding and contracting with temperature changes, which is normal. A loud, irregular clicking or rattling is not.
FIX First, identify the source. Unplug the unit, let it cool, and remove the basket. Gently shake the main body. If you hear a rattle, a screw or a piece of the internal housing may be loose. Check that the rear vent cover is securely snapped in place, as it's a common source of vibration noise.
IF THAT DIDN'T WORK The noise could be from the fan blade hitting something. Inspect the fan opening at the bottom of the cooking chamber for any small, loose debris (like a piece of onion skin or breading). Use a can of compressed air to blow out the chamber from the top.
HEADS UP A loud, grinding, or screeching noise from the fan motor is a sign of bearing failure. Stop using the unit immediately and contact support, as this is a motor issue that will only get worse.