Bang in 4x4 and now vibration

[Kwattro]

The last few weeks I've noticed a delay in my 4x4 engaging, then when it does it bangs into engagement. Sounds like it's more from the left side, but I can't be sure. Today when I used 4x4 there was a new vibration that I can hear and feel. Kind of a dull grind that tracks with road speed. When I disengage the 4x4 and back off the throttle for a second the sound goes away. I'm guess it's a hub going bad and probably hanging up on engagement. Is there a way to test it for sure? The truck is an '06 with the auto/manual hubs.

[Kwattro]

Today I manually locked the hubs and went for a drive. Without using 4x4 there was no noise at all, when I engaged 4x4 the noise and vibration returned. As I understand it with the hubs engaged in manual the entire differential assembly is now turning, including the axle shafts. However I'm not sure if the front drive shaft turns too? If it doesn't spin until the 4x4 is engaged then I would suspect a u-joint in the front drive shaft shaft. If it does spin all the time when the hubs are locked, I would suspect an issue in the transfer case. Does anyone else have anything to add?

[colinmacdon]

I don't have anything to add, but similar experiences. This is my first truck and I am curious to know how "loud" the drive train (t-case, front drive shaft) should be with 4x4 engaged.

I know when 4x4 is engaged I can definitely hear what I thought was the hub on the drivers side. It's quiet below 50 km/h (30 mph), but applying throttle after that it gradually gets louder. Once I'm up to speed with steady throttle I can hardly hear it, but letting off throttle makes it much more noticeable again. I always thought it was the hub, but based on your experience maybe is the u-joint.

I know on an icy road with 4x4 engaged if I slam on the brakes, I hear an initial clunk--I suspect its because the front brakes lock the wheels (on the first pump from abs), which in turn locks axle, then abruptly stops the front driveshaft causing a clunk in the u-joint (if there is some slop)

Also, in 4x4 when accelerating I hear a soft clunk in the 2-3 shift which is not noticeable in 2wd, so I had thought a bad u-joint was making it more noticeable.

I'm not even close to a mechanic, so this is just speculation.