2013 VW Passat, I have a popping noise coming from the rear differential when I decelerate. I rather diagnose and fix at home than drop my car at a shop. Any clue to the cause? Pinion, bearings? 

I have a popping noise coming from the rear differential when I decelerate.

For me, this comes from starchy foods. 

Diff mounts, inner/outer CV joints, U joints are most likely to cause clunks. 

First look for cracked CV boots, if all the grease sprayed out that'll be your problem. Otherwise jack it up and look for play in the diff mount bushings, or signs of mechanical contact between diff casing and subframe member