I've been noticing a noise in the front end of my truck. It's a 2008 Chevy 2500hd. It's only when in 4x4 and changes on acceleration or coasting. I hear it when accelerating mostly or when turning and the wheels are binding. I'm thinking it is in the front differential. I have jacked it up and spun everything by hand but can't seem to find anything noticable. I'm doubting it's a wheel bearing because it's only in 4x4. I drive a similar truck with the same drivetrain for work and the 4x4 is almost silent. So I know something is off on this one. Does anyone have any ideas on what to look for before I pull the differential?