2005 Dodge Ram limited slip keeps engaginig back wheels

I have a 1500 dodge ram big horn 4 wheel drive. The limited slip (or posi) keeps engaging and disengaging (whith a loud pop like I drove over a loose man hole when it disengages) at low ideal speeds when I turn. It recently had the (i cant remember what it was named) seal on the front of the rear differential where the yoke goes in replaced with a metalic color to the gear oil when it was cleaned out and replaced. The mechanic said there was no apparent damage but it did concern him and said that I may or may not have problems with it in the future. Have you heard of such a noise and action? What should I be looking for to repair this?