Hi,
When the car is up to temperature and between 75-85mph on throttle I hear a whine coming from the front of the car that I am fairly certain is the diff. I have checked the oil level and it's at the correct level and looks ok. Does anybody have any experience with oil additives to maybe reduce the noise, its not very loud but it is annoying. I don't currently want to go to the expense of a rebuild as it's not that bad.
Any advise would be greatly received

 

Are you certain the noise isn't wheel bearings?

 

Pretty sure, if I back off the throttle the noise instantly disappears. Also it is only present between approx 75-85mph if I go higher or lower it's not there

 

I agree: from what you describe, it doesn't sound like wheel bearings.