I know it's hard to relate a noise by writing about it but I need more information. Where does the noise sound like it's coming from? left side, right side. When does it make the noise? as soon as you put it in drive, when the car starts to roll, at a certain speed, on acceleration, on deceleration, when turning to the right, when turning to the left... what does the noise sound like. A hard knocking, a clicking noise, does it change with wheel speed?
have you checked your lug nut to verify they're all tight?
have you jacked up the wheels and checked the 4wd? there is a vacuum switch activated by the shift selector on the front of the transfer case. check to see if it's working normally.