2002 Dodge Ram is this a transfer case problem

My 4 wheel drive truck started making a high whine noise when I shifted into 4H today--when I turn, it almost sounds like metal tapping--seems to run fine--no noise in 2H--at higher speeds in 4H whining gets more quiet (maybe I just can't hear it)--is this a transfer prob, transmission prob, or both--had all the fluids checked--they are fine--