Clunk from the back

[saneesh8]

My Z have a clunk from the differential area. Diff mount and rear shock mounts are new. It happens when i coast to stop and at the end of stop when transmission engages. Also can reproduce with car on Ramp and putting in R-N-D or D-N-R. Can see the differential moving up and down while doing this (with new mount), but the clunk is there. The mount welding is ok and it sound like CV. No rip on the boot (inner), but it is dirty (kind of like oil and then dust). How to isolate CV issue? When car in ramp, no radial play ( i cant rotate), but it moves horizontally towards both wise (diif and to wheel side). Any clue?