I wrote a long reply to your problem. What it could be is that the rear drive shaft needs to be lubed behind the T-case. But grease will shot out the top of the splines not lubing it self. you need to plug the hole in top of the slip yoke. than add grease. The drive saft will push the grease up hit the plug and travel down the splines and no more clunk. Check the FAQs for more answers.