I have a 54 reg S Type SE Diesel Luxury Package 101000 miles. For the past year the differential seems to be slightly noisy with a whine on part throttle between 55 and 70 mph. it has not got any worse and it is quite easy to live with, but it would be nice to have it completely silent. Is it something to live with or would it need an expensive diff rebuild? The differential oil has been changed to see if it would cure it but to no avail.