Do you hear that when turning and moving, just turning and standing still?
One thing to consider is tire size. Your vehicle does not use a viscous coupling like they do in the Dodge Caravan or Ford Aerostar. You have a regular transfer case meant for part-time use being used full-time. Driving and turning puts a lot of stress on all of the drive line components. The only time the stress is reduced is when you're driving straight ahead. What is a killer for this is installing different size tires on the front and rear. Even buying a pair of new tires one day and the other pair of the same size and brand a month later has been well-documented to cause severe damage. That is simply because one run of tires can be slightly different in size due to use of a different mold or different manufacturing plant. It is very important that you buy four new tires at once for your vehicle.
When the tires are mismatched, the stress results in damage to the transfer case, typically not the front or rear differentials. A tool that can be very helpful in locating noises is called the "Chassis Ear". It is a set of six microphones, a switch box, and a set of head phones. You clip the microphones to various suspect points, then listen as you drive. Be aware that many mechanics have never heard of this tool or seen it. You might find it at an auto parts store that rents or borrows tools. I can post a link to it from Mac Tools too if necessary.