1999 Grand Cherokee Limited 4WD

My 1999 Grand Cherokee seems to be staying in 4 wheel drive all the time. It is a 4.7 v8 with 119k miles. When I turn sharp to the right or left the tires bind and I hear a loud popping noise. I have checked the fluild levels in differentials and transfer case. Any ideas on what could be causing this?


******This turned out to be my viscous coupler. Fairly expensive fix.