You need to remove it, disassemle it and rearrange the plates. There are alternating drive (D) and axle (A) plates. The diff is most likely shipped in the 100-percent locking configuration, which, if you continue to call the differential plates D and the axle plates A, means each side has the plates stacked DADADADADADA. Every time there is a D next to an A, there is an active friction surface. This could also be causing that "popping". If you swap a few plates around and stack them DADAADDADAAD, you knock the number of active friction surfaces from 11 down to 8. This configuration is called 60 percent locking. Also, check to make sure the right lube is being used. Nismo should be able to tell you what kind of lube to use and can also tell you whether or not you need to add a bottle of "friction modifier" (an addative sometimes added to LSD's).