2008 H2 VIBRATION IN FRONT AXLE

[blackhawk29]

My 08' has developed a vibration / growl somewhere in the front driveline. It happens from 50 to 70 MPH (and above) when on the throttle and when letting off the throttle. It is more apparent when coasting, say at speed then letting off the gas. I know it's not in the tires, probably not the CV's, and happens when in both 4x4 modes. could this be in the transmission or transfer case. called dealer and they said never heard of this issue. Any ideas or similiar experiences?