?transfer case problem?

I own a Jeep Grand Cherokee - when I go over 45 my car makes a cranking/banging noise. I took it to the Jeep dealership and at first they said it was my driveshaft - so I got that replaced - turned out it wasn't - it's still making that noise. Then they said I needed a new transfer case because it's leakinga nd that the whole case needs to be replaced. Not trusting the dealership now seeing how they already got $900 for something that wasn't even the problem, can any one tell me or give adivce - if it's actually the transfer case.

Quadra-trac or Select-trac?