I have a 86 Samurai and when I put it into 4 wheel drive it vibrates a little at first and gets worse the faster you go. When you hit about 30 mph and you let off the gas, there is a horrible clanking and grinding noise. I changed out the transfer case and I get the same noise from the new one. I checked all of my u-joints and they are good. The noise is the same with the hubs locked or unlocked. It does it in 4-hi or 4-lo. The grease under the hubs in the axles looked good and didn't have any metal shavings in them. I know it could be bearings, or ring and pinion, or unbalanced drive shaft but I was wondering if anybody has had this problem and what it turned out to be, or any quick ways to troubleshoot what it could be.