Grinding noise from front axle

My 99 dodge Ram 4x4 has developed a grinding noise from the front axle. This happens only in 2 wheel drive and will stop when shifted into 4 wd. The noise appears when you hit a bump. Could this be a linkage problem? I have replaced the front u-joints and checked the front end. I am stumped:banghead: Does anyone have any ideas.

If you have a bearing buddy lube the front wheel bearing. Try rotating the wheel by had and check for noise.

I have checked the bearings and they appear fine.

You can not grease the bearings, they are sealed units. Raise the truck and grab the tire at 6 and 12 oclock. If it wiggles back and forth, the bearing or a bj problem is present.

Yes, I know. I have checked for play in the hub and Bjs.

Ok here is an update. I took the truck to dodge and they said it was a u-joint. They wanted $435 + to change out. I replaced and the noise has gotten better but still there there. It is a vibration and growling noise. Any ideas.