I was travelling happily at about 70mph when I heard a strange whining sound. I slowed to take a listen as it got noisier, then as I cut across 3 lanes of traffic to pull over the diff locked solid and I slid sideways to a halt with lots of tyre smoke! The question is, why did this happen? With both rear wheels jacked up I can turn the wheels, but even with one shaft disconnected they still won't turn on the ground. Any good guesses?