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

just a guess here but probably something in the front differential I doubt it is the cv joints since on a Silverado they turn all the time but there is no torque on them in 2wd it could possibly be in the front drive shaft or in the transfer case but you would probably hear/feel that under your feet more then from the front end. if you can get all 4 wheel off the ground and get someone to put it in 4wd and accelerate you can use a mechanics stethoscope and listen to the components and narrow it down