Yes,I've heard that they can be a bit loud but mine has really been quite ok until this year. I checked a bit more yesterday and the clunk is very audible from inside the diff. The clunk is rather sharp and seems to come from where the ring & pinion is. It might be a problem with the backlash. The propshaft and driveshafts seems fine and quiet.
From pictures I've found online it looks like the unit is produced by O.M.R so the hope of easily obtainable ZF-parts is out.