Hi, I have a 2006 GMC Yukon, 4x4 with the 5.3 liter Vortec and Autotrac. It has 90,000 miles, and lately I've noticed a strange clanking or ratcheting sound coming from the rearend, sounds like metal on metal. I've narrowed it down to mainly or only happening when put it in reverse to back up my driveway. I never hear this particular sound in forward, but when I put it in reverse and hit the gas moderately it sounds like something is clanking or ratcheting from inside the rearend. Now I know obviously this is not a good sound, and I need to take the cover off and check out whats going on,but its done this for awhile now with seemingly no symptoms while driving. But lately, under harder acceleration, its made a sound almost like worn u-joints, and I seem to be getting a slight vibration at high speeds. I'm thinking possibly the G80 locker might have let loose and it has something to do with that? Any mechanics out there have this problem come up? I'm gonna take the cover off tomorrow.