I'm not too active on this board, so I really appreciate anyone that helps someone like me that doesn't contribute much. My mom has a 99 JGC, 2WD, 4.0L. It has 80,000 miles on it.
Lately, my mother has been saying that a whirring noise is coming from the back of the Jeep. I realize that "my car is making a noise" is the hardest thing to diagnose over the internet, so I'll do my best to describe it.
Its definitely a noise that increases in pitch with velocity. You can only hear it when there is a torque on the driveshaft (i.e., when coasting, it goes away). Its loudest while accelerating (I've only heard it once, and I wasn't driving, otherwise I would have put various loads on it to see how it changed). If you throw the tranny in neutral, it goes away completely, so its not engine related.
The noise doesn't decrease in pitch once you shift, so I think its only dependant upon the angular velocity of the driveshaft, and not the transmission.
I change the diff fluid at 60,000 miles with 75W90 Synthetic Gear Oil. At the time, the old oil looked old, but nothing out of place. I checked the rear diff to see if perhaps the oil had leaked out, but the area was bone dry. I did not have time to climb under the car and actually check the diff oil level.
At 78,000 miles, I flushed and filled the trans and put a new trans filter on. After that I drove the car for about 3 days with no incident before I went back to school.
My guesses are either that there is something wrong with the differential, wheel bearings, halfshafts, or mabye the U-joints (I don't even know if the car has U-joints).
Oh, and the diff is just a regular open diff, no LSD.
Anyone that has any idea of what this noise might be, your experience is greatly appreciated. If I can give you any more information, just ask! Thanks alot guys!