2004 Dodge Ram Squeeking from Rear End

I have a 2004 Dodge Ram that is squeeking from it sounds like the rear of the truck. When you slowly move it has a squeek everytime the drive shaft makes 1 revolotution. You eventually get up to enough speed where the sound goes away. Any ideas? The U joint looks to be in good shape and has a grease fitting that is taking grease. Should I replace it just as a shot? I have put a jack under the rear end and replicated the squeeking by placing the tranny in nuetral and hand spinning the tires. I have also check the rear diff fluid and it is good.