Renault Megane noisy diff

In the 22,000 km I have done in my 2008 Renault Megane auto sedan I have made seven trips back to the dealer complaining about a noisy differential. The service manager agreed the diff was noisy and a Nissan service adviser also agreed it was noisy, but that Renault would do nothing about it as if they replaced it could be worse than the one in the car. I then went to consumer protection and they agreed the diff was noisy and that they would talk to the dealer. The dealer's reply was that the noise was a characteristic of the car. If this is the way Renault treats customers I don't think they have much chance of success in Australia.