Listen for the vibration as the fan shuts down if the vibration changes as the fan slows down then it's likely the sleeve bearing on the fan.
Call Girard and get the part number for the fan if you can replace it yourself. Good luck. Post your progress please.
2004 Ford F550 6l Lariat SuperCrew, Fontaine Bed,
Link Systems Air Ride
2011 Sterling 32RL with Michelin XPS tires