2000 Grand Cherokee 4 wheel drive not workig

4 wheel drive not working in full time mode, drop into low and it will work but get a bad klunking sound. Klunking is coming from up front, transfer case or wheel, really cant tell. Might be from front pumpkin. This has the quadra all time 4 wheel drive. Any ideas on what to look for?

Anyone have any suggestions i can check for ?