CHEVROLET TRAILBLAZER TRANSFER CASE

I Here A Humming Noise In The Front Of The Truck. It Sounds Like A Hub Bearing But I Dont Know For Sure It Could Be Some Kind Of Other...

When I Am In 4 Wheel Drive Or Auto (which Automatically Engages 4wd When Needed) I Hear A Noise That Sound Like Jets Landing And It Is Worse...