My 2001 is making an loud intermittent binding / chirping noise when I put it in 4WD. It is the standard Auto 4WD/2 HI/ 4 HI/ 4 LO setup. The 4WD still works, and it seemed to get better as I drove it, however still there when accelerating and turning. The 4WD has not been used in months and I have never had a problem before. The service light has not come on either. Any ideas ?