I have a grinding noise coming I believe from the front differential in my 94 F-250 4x4 351. The noise is only heard in 4wd when accelerating up a steap grade. This is a pretty loud grinding noise. I took the auto hubs off and everything looks fine. The noise seems to come from the front, center, so I do not think it is the transfer case. What could be causing the noise and what do I need to do to fix it? Thank you very much for your help.

Just noticed this may be in the wrong section. I should have posted in the differential section.