2001 Z71 front diff (?) noise

Recently, my 2001 Z71 started making noise from somewhere in the front end. I think it may be the diff, but I can't be sure. It only happens in 4WD (auto, hi, or lo) and when I shift back to 2WD, the noise stops completly.
The frequency of the noise increases with road speed.
I changed out all the fluids (except for the tranny) and replaced them with synthetic front/rear and the Autotrak II fluid for the transfer case.
The problem seems to only happen once the vehicle and all it's fluids get up to normal operating temperature. I'm not sure where to go from here (except to the shop!)
Any and all help is appreciated!!
shakman9999
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sounds like the output bearing for the front output shaft since it only happens in 4wd. -- Mad Dog

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