Just done the same, fitted new rear center diff mount and its still clunking
I had a look at my prop and grabbing it and push/pull and it clunks so that is my next suspect (rubber donut that the bearing sits in is fubard at a guess). OEM is ££ so I am going to use a bmw one as its £15 or £30, just make sure the propshaft is aligned straight if you fit a new bearing/mount thing.
As above the gearbox mounts.