four wheel drive problem 4h and 4l

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hi i have a 4x4 2003 dodge durango it has 99688 miles in it. a few days ago i turned on my 4x4 switch on high and i worked like a champ, yesturday i turned it on and when i start to make a turn it sounded like my timing belt was too loose and when i turn my 4x4 low and my truck wont go. can it be my timing belt or what can it be? please HELP