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.