GMC Repair: 2001 Yukon XL 4WD, wheel bearing, front axle

Question
My Yukon started making a loud rumbling sound with a vibration starting at 65 mph. Garage determined that the front driveshaft was spinning in 2WD HI and causing the problem. They said the transfer case encoder motor was not working so that was replaced. After replacement it still had the same problem so the garage said the new encoder motor was defective and wants to replace it again. Called Chev garage and they said it sounded like the front clutches in the transfer case were "tight" causing the driveshaft to spin and that the encoder motor was not the problem.  Auto 4WD, HI 4WD, and LO 4WD work fine. Any suggestions?  Any idea what is involved to "loosen" the front clutches and cost?

Answer
So the 4WD works, but you just have noise at around 65, would you describe it as a growling type noise?  If so, first check would be to see if your front tires are cupped on the inside edges, that can make a growling noise, if the tires are good, it could be Front Wheel bearing, I am not sure what the mileage is, but I have done many.  If the wheel bearing check ok, meaning they are tight and noise free.  Then it may be time to take a sample of fluid from the Front Differential, if it smells really bad, or is badly discolored, most likely you have an issue with the clutches and bearings, best of luck.