Gear-type crunchy noise

[soane]

Hmm, my Macnum gearbox has developed a strange gear-slippery crunch noise when accelerating. Lasts a couple of yards then goes, the car seems to accelerate OK otherwise. I pulled the box apart the other day, all the gear teeth were there, the diff seemed a little under-greased so I applied a little more, rebuilt to what I thought was tight, rebuilt the slipper and test - massive slip. Tightened the diff screw and all was well but the noise was still there. I've never built a ball diff before but I realise I can't over tighten it as I'll push the balls into the thrust plates. Any one got any advice?