I have the same final drive noise,came in at approximately 17ks and was told at next service it was normal and not to worry.I have now done 48ks and left it with Gary MacMillan Toyota for assessment.The reply was.There was a periodic whine hardly noticeable.To repair,they would dismantle and inspect then order parts,which could take up to five weeks.This sounds more like a big effort to put me off than anything else. I think I will discuss this with Toyota directly as it sounds like a fairy tale that should start with,''Once upon a time''.