Ah, sounds like you've got a different issue than what Ihad. I looked around online when Ifirst got my MR and the dogbone clicking seemed to be a halfway common issue. IIRC, others swapped dogbones/stub axlesand someoneelse suggested to lower the ride height. A friend of mine also bought a MR and his didn't click at all. Go figure.
I don't know if a spring would necessarily help? If I understand correctly what you mean, the spring would be inserted into the cup of the stub axle, then you would install the dogbone. I don't think it would do any harm, but I would be wary of pushing the dogbone too far out of the cup, so the the dogbone could become disengaged. Although Idon't *think* the dogbone can shift far enough laterally to come completely out of the cup.

My experience when adding CVD's is another reason why I suggested filing down the drive pins on the dogbones. Ibought the CVD's for the 18T/B/MT only to discover that theendwhich goes into the diff outdrive hubswouldn't fit because the drive pins were too long (Associated uses outdrives that are slotted completely through the wall, HPI's are only slotted internally). Filing did the trick. I should have added that a little goes a long way...if you do try the filing route, I would do it in small steps, and try to remove an equal amount of material from both sides. You wouldn't want to file down to the nub or have grossly mismatched drive pin lengths. Just enough to stop the clicking, but still have positive engagement.