Most Rovers (at least all 5 that I've owned) have a minor whine when you take your foot off the gas. If it is minor I would say it is normal. If it is a significant noise then you probably have a problem and just need to start looking at all of the drivetrain components. I'd look at the front diff first since that is the one that was removed. There may have been a reason for it.

 

cheers going to change the rear diff anyway because of the bits that came out. will a 4 pin diff fit if it turns out to be a 2 pin diff and what will needed to be changed if so?