Diagnosis
That noise usually means something is touching or interfering with the convection fan blades at the back of the oven cavity. It's often a piece of food debris or, more commonly, the metal mesh from the air fryer basket if it's gotten bent.
How to Fix It
Unplug the oven and let it cool completely. Pull out all the racks and trays. Get a flashlight and look at the circular fan housing at the very back wall. Slowly rotate the fan blades by hand and look for anything stuck between them and the housing. Use a soft brush or a damp cloth to gently clear any debris. Also, inspect your air fryer basket—if the wire mesh is warped or has a loose strand sticking out, that's your culprit.
If That Didn't Work
The fan motor's bearings might be wearing out or there could be a loose component in the fan assembly. Listen closely to pinpoint if the buzz is coming from the center of the fan. If it is, the unit likely needs a professional repair.
Heads Up
Always let the fan come to a complete stop before opening the door after cooking. Jamming the door open while it's spinning at high speed can damage the fan motor over time.