The whining noise and leakage you are experiencing in your 1999 Jimmy are most likely caused by a problem with the transfer case. The transfer case is responsible for transferring power from the transmission to the front and rear wheels. When the transfer case is in 2WD, the front wheels are not engaged and the power is only sent to the rear wheels. This can cause the transfer case to make a whining noise as it is not properly lubricated. When the transfer case is shifted into 4WD, the front wheels are engaged and the power is sent to all four wheels. This reduces the load on the transfer case and the whining noise should stop.
The leakage you are noticing under your car is most likely coming from the transfer case or the front axle. The transfer case and front axle are both filled with gear oil, which can leak out if there is a problem with a seal or gasket.
It is important to have your Jimmy inspected by a qualified mechanic as soon as possible to diagnose the exact cause of the whining noise and leakage. Driving with a faulty transfer case or front axle can cause further damage to your vehicle.
