Hello everyone, I have a 2004 rubicon that vibrates starting at around 45 mph. I tried replacing the tires first with no resolution so I removed the front drive shaft and the vibration went away. I since have had the shaft shortened (to accommodate the 4 in lift) and balanced. I reinstalled the shaft and the vibration came back. I have since replaced every u-joint in the jeep and still the vibration persists. Also, the vibration goes away when 4wd is engaged. I removed the front diff cover and everything checks out. No loose bearings, chipped teeth, etc. Any thoughts or suggestions? Thanks.