I had the same sort of noise develop on my 4WD FEH at around 12000 miles. It sounded like a fan belt coming apart but was not directly proportional to engine RPM's. It sounded serious and lasted about 5 miles and then stopped. I tracked it down to a label that was attached to the drive shaft that gradually came unglued and finally flew off after hitting the chassis with each rotation of the drive shaft. I crawled under the car and found the adhesive from the label which was about an inch wide and possibly 3 inches long around the driveshaft roughly beneath the console and was probably a part ID label.