This is normal for your type of 4WD.
You are binding up your drive train since you have a part-time 4WD system. Don't use the 4WD unless you have bad traction conditions and then only when you need it.
Your 4WD system locks the front and rear wheels together in the transfer case. When you drive perfectly straight, your front and rear wheels will turn at exactly the same speed. This is good. However, normal driving makes you perform turns. When you turn, your front wheels have to go farther around the turn than your rear wheels and they are no longer turning at the same rate. The front drivetrain is no longer in synch with the rear, but your transfer case is forcing it to be in synch within the transfer case. This is why you are binding. You are putting alot of stress on your transfer case and other drivetrain components.