Mitsubishi Triton clunking noise

The Mitsubishi Triton we bought new in 2013 has made a clunking noise ever since it was purchased. It doesn't do it until the car is warmed up, but the longer you drive it the louder it gets. The centre bearing was replaced in an attempt to fix it, but it didn't and we have been directed towards the differential. But Mitsubishi says it's in spec and won't do anything. A Mitsubishi rep who drove the car had said it was normal, but we don't believe that. We have had it checked by a couple of diff specialists and whilst the diff backlash is within the spec it is at the higher end of the scale. Is there any advice you can offer or any one whom you might be able to direct me to in order to help get this resolved?