Hard to tell, 4lo is direct coupling I think. Could be broken front axle, front diff, front driveshaft, transfer case chain. I've heard of some that have destroyed a front axle half shaft. But you are going to have to do some troubleshooting. Get under and take a look. If nothing obvious, jack one front wheel off the ground and try to spin it, if you don't notice anything unusual, put it into 4low and try to spin it. You shouldn't be able to turn it.
2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6, 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac