Hi all, I'm new to the site. I have GMC C3 (01-only yr). It has 123k. I've been deployed for almost two years. Shortly after starting to drive it again it I began to feel a vibration coming from the drivers front side and a very mild groaning like the FWD of a common 4x4 makes that is engaged only occassionally. That has turned into also a rotational squeek and a metal clinking when you change momentum from braking to acceleration. I assumed the LF drive axle was going bad even though the boots were intact. I visited a guy who specializes in Drive Axles; I've used him before on my rental cars and I believe him to be an honest guy. He said those drive axles virtually never go bad unless the boots are torn. He inspected the drive axle and said it was not the problem. His diagnosis is the front differential going bad. He suggests replacing it with a used one...as they are the same as the Escalade and are quite expensive. He quoted me $2,250 to install a 40K used one w/warranty. Anyone have experience with the C3 AWD system? It has always been the smoothest, quietest AWD I've ever driven. Anyone know where to look for that differential new or used?