2000 Suburban with vibration

I've got a 2000 Suburban 1500 4WD with the Auto 4WD. I'm running into a vibration at highway speeds along with a clicking sound at idle speed which speeds up and slows down with speed. I've discovered the u-joint on the front drive shaft where it connects with the transfer case is worn and has play in it. Could this cause the vibration?

Also, there has been some debate about the front drive shaft when talking with other folks about this issue. The front drive train spins any time the vehicle is motion, which is to say the front drive shaft spins as the truck goes down the road, correct?

Worn u-joint will make noise and cause vibration.

I don't know for sure on the subs, but most 4x4's these days engage/disengage the front diff, so yes the front driveshaft will spin all the time. It may only function that way when in auto mode to give faster engagement. Does it have the same symptoms while driving in 2wd?
Another thing that can cause noise and vibration is the cv-joint in the front half shaft. If its worse when turning to one side or the other I'd lean towards one of those being bad.

If you are in 2W HI, the front drive shaft should not spin when driving.