Sounds like the fan bearings are shot. When it starts to squeal, It is
usually too late to oil it. However, you can try if it has oil ports
on the side of the motor. Add 20 drops of 20 or 30 weight
non-detergent motor oil to each port. DO NOT use WD40 or sewing
machine oil or penetrating oil. Use a squeeze bottle with a small
nozzle on the end to get the oil in.

If that doesn't help, you are looking at $200.00 to $350.00 depending
on rates in your area. Should take 1.5 to 2 hours to diagnose and
replace the motor. You will pay more if the fan blade cannot be
reused.

Stretch