Nissan Repair Questions? Ask a Mechanic for Answers ASAP
hey there thanks for the question.
There is certainly a few possibilities here, my first concern would be an issue with the transfer case itself. have you inspected the case for leaks?
Secondly I would check the front driveshaft u-joints, usually when the front u-joints are extremely stiff or worn there will be excessive vibration in 4wd. If you switch back to 2wd the vibration is still there its just SIGNIFICANTLY less vibration. So if thats the case start at the driveshaft and u-joints up front.
If the vibration ONLY happens in 4WD then you want to consider the transfer case and front axles as well.