I agree it is probably the bushings/bearings in the fan motor, they are dry. usually not serviceable but I have bought some time by taking the motor out and dripping some oil on the motor shaft next to the bushing and turn the fan by hand and let some oil wick into the bushing. There is usually no way to lubricate those motors and a new motor is the fix
Othertonka
2004 Southwind 32VS 8.1 Workhorse chassis
2002 CRV Toad
U. S. Gear Unified brake system
Retired Fire Captain, SFD