I have a 98 Cherokee sport 4.0. Couple weeks ago I starting getting this weird knocking/clicking when accelerating and stopping. I also had a vibration when going any faster than 50 mph. I greased up my front drive shaft (which was empty of grease) and the problem went away for about a week. Now the noise and vibration are back. (FYI I had my tires balamced and rotated.) So I tried greasing again but it did nothing. I was thinking about just replacing the u joint first and if that doesn't fix it then doing the whole drive shaft. But is it even the drive shaft causing this or could it be something totally different?