I've got a fullsize 89 blazer with an automatic 700r and auto lock hubs, that has, on occasion, a rotational clunking. At first I thought I had driven over a brick, then it did it again and again. I got it at a police auction, it seemed to have been parked for quite a while, bottomed out, in the middle, over a large mound. The previouse owner had run the motor dry of oil and seized it. A few days of penetrating oil and manual turning with a bar, and amazingly it runs fine. At low speeds,both in drive and reverse, there is sometimes a clunking that seems related to speed. As I increase speed so does the clunking, until, at about 15 or 20 mph, it stops. It's 33" tires with no lift and I know that the clunking isn't the fender interference. That's just on turns and is quite distinctive. My joints all seem fine, there doesn't seem to be any play in front of or behind the transfer case. Just the tiniest play back and forth on the rear drive shaft. The front axle joints show no signs of wear and I don't see evidence of any loose suspension bolts or a loose transfer case mount. Having opened the 10 bolt rear differential I know that it's an open differential with all of it's teeth intact. The fluid was relatively clear with no broken bits, just the fine stuff stuck to the magnet and at the bottom. The bugger is that it's not constant or predictable, and it hasn't done it in a month. After having been much more frequent, like 1 out of 2 times driven, and then less frequently. So it's difficult to pin down. Any thoughts?