I have an 01 Jeep Grand Cherokee 2wd 4.0l. I noticed a ticking/clicking sound that speeds up as I go faster. It almost sound like there is a piece of metal stuck in the tire that's hitting the ground as the tire turns. I first glance I didn't see anything on any of the tires and nothing looked out of the ordinary along the drive shaft. Could this be something wrong with the differential or maybe tranny?