Need help on my Silverado.. Grinding.. Whirring sound up front in 4WD

My guess from the sounds of it, would be a bearing within the front differential.
On the basis that I'm asuming that it is IFS and that you mention that the sounds are in 4wd, ...and not in 2WD, ...here I am asuming this as well.
I had to have a bearing replaced in the front diff. of my '03 Sierra a few years back, ...had a nasty whirring/groan sound while in 4wd and sounded normal in 2wd.
I doubt it's the CV shafts, if the noise changes from 2wd to 4wd as they are always spinning anyway