After about 3 years of use, the fan in our oven started making noise.
I had success with lubricating the fan through the inside vent... without taking the oven apart!
Place the oven on its right side. With the door open, the fan and vent will now allow a silicon spray (with a 'straw' attachment) to be directed through the vent to the center hub without dripping too much. After leaving it set for a few minutes, I plugged the oven in and turned on a cook setting that used convection and there was absolutely no noise.
This may change over time if the silicone dries, thickness or coagulates but... I will try another 1 minute fix before attempting to disassemble the metal housing.