Knocking sound inside differential

[heiwaz]

Hello, I hear a stranger noise when I shut off the engine and sometimes when I go in first gear o rear very slowly and low revs.

I discover that when I move the axle (left or right), I hear the noise inside the differential, it look like a clearance, what do you think is the problem?

I recorded a video to hear the noise I explained:

https://youtu.be/BVdZbvXpN1s

Porsche boxster 986s