Revolving deep grinding noise coming from front in 4wd

I have a 92 Jeep Cherokee with a 2wd, 4 parttime, 4full and 4 low transfer case. I have started hearing a loud revolving grinding noise coming from the front. Makes small clicking, grinding noise in 2wd but gets a lot louder (deeper) in 4 Full. Seems to shift between 4 full and 2wd okay. As a test I removed my front driveline and drove it for a month and as soon as I removed it there was no more noise. But now its snowing again and I put it back on and switched to 4 Full and it started grinding. A year ago I replaced both front U-Joints in my front axle and and I replaced my axle side U-joint on my front drive shaft. So I don't think that it is any of these. Any ideas? I desperately need my 4wd working properly in these winter conditions.

possible front pinion bearing. Can you move the yoke up and down or any gear lube leaking from the yoke area?

There isn't any lube leaking from the yoke and I don't think that the yoke moves. Could the double cardan on the front shaft be the problem? I have never replaced it.

Do you feel real bad vibrations ? Is the Tcase full? how many miles does it have. Bad carden you will surely feel like the shaft is falling out.You should also be able to move it if it is bad. Remember when you check for play in the drivetrain that the trans is in neutral ,motor off and on level ground.