How can you tell if your diff is on the way out???

Hi,
Just had my Freelander 2 in for its service at an indy garage, and it has started to whine from the back, was not too sure if it wasn't road noise, so asked the garage to check it out. The say its either the rear wheel bearings, as they say that they can feel a little play/drag in them. Or its my diff, they suggest changing the wheel bearings first (£520) and if that does not work then its a new diff!! read the write up about the known problem with the diffs so I am now a bit worried.
Does anybody know how I can test to find out if its the diff at fault or the rear wheel bearings???

Push it hard into a bend, when safe to do so, if the noise stops when steering left its the left side bearing or vice versa. Rears are more prone to go but your garage will have indicated which one has play. Rear brake shoes stick on the FL2 and can whine. If your indi can't tell the difference between a wheel bearing noise and a diff go somewhere else. Wheel bearings are £60 max so unless they suggest swopping out all four there taking the P**s.

That does seem extortionate to me!

Thanks I'll have a go at the driving into a bend and see what happens, the garage told me
both rear wheel bearings would be changed, according to them it would be 6 hours labour charge! and the bearings would cost £69.28 each + vat.