Credit Marcos P. for being frustrated enough to figure out this solution to his fan noise
The blower assembly is a tower-like assembly of two blower sections within the same vertical axis. The top one does have an air filter (can, or should it be ever changed?). The bottom blower air intake apparently has a small air gap in relation to a bottom square cover tray and is the noise culprit.
There are three phillips-slotted plastic push pins holding a square plastic tray below the glove compartment. Insert a philips screwdriver and with a quarter of a turn the pin head will stand out, just barely enough to be pulled with your fingernail. After the screw part is pulled out, the whole pin can be removed from each hole. After the three pints are removed, the plastic tray can come forward and be put aside. The bottom air intake will be exposed. You can now remove any foreign objects that might have been sucked in and are causing noise. That's where I found a fairly beaten post-it note.
Caution: Do not insert your hand there with the fan on - the blower is quite powerful and the blades are sharp. (Don't ask how Marcos knows this, please)
Reassemble the bottom tray by aligning the two integrated pins at the rear of the panel with the mating holes. Then lift the tray up to align the three holes for the loose pins that you removed earlier. Push the pins into place. This can be a bit tricky! The holes need to be lined up perfectly, and the pins need to be prepared before they can be inserted. The three pins have two parts, a screw part and a flange part. If you separate the screw part and the flange part (like you did to remove them), the tines on the back of the screw can be pushed back together to allow them to fit through the holes. Line up the plastic panel holes with the mating holes in the metal dash piece, and push the loose pin assemblies through the holes. Then press the screw part of the pin back into place. Pressing in the screws causes the screw's tines to flare, securing the panel.
Enjoy silent, cold air flow.