Canon pixma mp780 load squeals when paper returns

Remove the duplex unit, there is a bundle of gears in the back of it on the side. Get grease if you have it, otherwise you can use WD-40 or Vaseline and cover them really good, do not spill the WD-40 on the wheels (it'll put oil spots on the paper.) See if this stops the noise.

If it does, you can do this every few weeks as needed or get the grease and use that on the gears for a more permanent fix.