I have a slight thump when I come to a complete stop and start to accelerate on my 02 Frontier 4x4. The thump is not that bad it just annoys me every time I stop and accelerate I feel it a little. I read on here it could be the slip yoke and there's a grease fitting on the drive shaft for it. Can someone please tell me if it's ok to pump grease into the fitting on the slip yoke, and how much should I pump into it before I should stop? Any help would be much appreciated. Thank you.