I had my rear diff on my 4.2 SC rebuilt with all new bearings, seals and correct oil. The old bearings were literally shot.

I am however, still getting a slight whine from the rear and not sure if it's diff related or wheel bearing.

The car's going in for an Indy service on Thursday, so will get them to investigate, as well as servicing/replacing the suspension exhaust muffler jobby.

I'd be surprised if it is the diff, given it was comprehensively dismantled, cleaned and rebuilt (got the pics to prove it), but could it be that something wasn't set correctly ? How can the indy check it without being under the car whilst it's driven !

Any thoughts on the topic gratefully received.

There are devices that can be attached around the running gear to help pinpoint noise sources. Whether the indy in question has such a kit is the question. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed