Low Speed Front End Noise when 4WD Engaged

[gunthernsons]

I'm new to this forum, but not new to Tahoe. I'm looking at a 139k mile 2005 Z71 Tahoe from a local dude. During my test drive today, I discovered a noise that appeared under the following conditions:

• 4WD Engaged
• Low speeds (3-12 mph)
• Brakes not applied
• Sounds like a brake grinding (but brake not applied)

This problem is not present when switched out of 4WD. I'm looking at getting back into Tahoe after a tree fell on my Trailblazer but I need to to know if anyone has any ideas of what this could be. I have searched a bunch and have come up with a few stretches, but no real possibility I can check for when I go to check it out again. Thanks a bunch for everyone's insight and I cannot wait to get more involved here!

 

[Mvfootball1]

Sounds like a front differential going bad. Does it do it at regular driving speeds as well?