Spools are described as NO differential action. Open differentials are completely free to rotate in either direction. the Limited Slip differential is somewhere in between those 2 extremes as it has a clutch pack friction system in place to make it harder for one axle to rotate at a different speed than the other side. You can leave the pressure on the clutch packs loose and it will be more like an open rear end. If you tighten up the pressure on the clutch pack it will be more like a spool. If the clutch pack is set up very tight, the axles will actually twist and wind up like a spring on turns as the tires are sticky and the clutch pack resists any differential action. If you hear popping it can be the axles releasing the "twist" as they return to straight. The twisted axles will release this force in two possible ways. Either the tires slip or the clutch pack gives in and allows the force to be released by movement inside the differential. Either way, the axles can "snap" back to straight and you can hear the popping sounds. I beleve JRE is suggesting stiffer axles that might not twist as much as the factory axles so that solution "might" help in your situation. Stiffer axles will resist winding up like a spring and that will force the tires or clutch pack to slip before anything can wind up reducing the "snap". Given your current setup, the differential clutch pack is set tighter than you want now.
The way I see it, you can try the (cheap and easy) friction modifier and figure 8's again and if that isn't getting it done then consider sending the posi back and have the clutch packs loostened, or try adding some stiffer axles (that you may need in the future anyway).
Just trying to help here.
-Mark.