Talking to a mechanic is like talking to your significant other: they can't read your mind. You must articulate (describe) clearly what is the problem or symptoms. Put your vehicle through several controlled tests so you can describe exactly what the vehicle is doing and when it does it. For example, turn corners, back up, engage and disengage the 4WD, go up and down hill, and determine exactly what the vehicle is doing under these conditions.
A good example is a vibration. To pin down a vibration try several tests. Drive it fast. Drive is slow. Get on good pavement and drive it. Find out if it happens at certain speeds more than others. Put it in and out of 4WD and drive it. Go someplaces where there are curves and see if it's worse or better. Put it in and out of neutral and make it coast and see if it goes away or gets worse.
What you're trying to do is to give the mechanic enough information to save him time tyring to pin down where to start looking. This saves you money. The more you pin it down for him, the less time he has so spend digging and testing.
So once you have the problem isolated to certain conditions, describe exactly to the mechanic what you did and what you found.
Where is a good place on the Internet to talk about 4WD stuff?