I've been looking over the forums and haven't found yet exactly what I've got going on. Everything is perfect while driving in 2 wd. When I engage my manual hubs and go into 4 wheel drive (high or low) I have an awful clunk and it shakes the whole truck. If I creep along very slowly with little torque it it's there. I can only go about 10 kph because it gets so loud and violent. I've rebuilt the hubs and they are fine. Fixed tie rod ends and such to make sure all is tight. I thought noise was coming from passenger side. But now I'm leaning towards right under the engine (transfer case?) it just happened out of the blue. Any info or ideas would be great. I am no mechanic but I do have access to a shop. ( rebuilding hubs was a little scary, but successful). When i put truck on hoist with tires off the ground it is fine no sounds nothing. Tires are spinning fine. Oh and it's all the time.. Driving straight/turning/reverse...

 

Check your CV's , front drive shaft u joints. Could also be the diff or even play at the end of the axle housing