One of my colleagues has a 2003 impreza WRX wagon whose rear diff makes a clonking noise when maneuovring at full lock when warm. The local dealer said they used to get a few like that, to fix the problem they'd drive round a carpark in circles until the diff wound itself up then freed itself with a bang. Any ideas on a more sensible fix?

 

Differential oil need changing, driving it around the car park isn't going to fix anything permanently, I can see why they mentioned it but its a little half arsed ;0)