I had a knock from the rear end. I replaced the diff, drive shafts, shocks and various bits and pieces to no avail. Drove me nuts for months, in the end i bought some chassis ears and found the problem in less than 5 minutes. Was a loose bolt on one of the brackets that connects to the subframe. I still have the chassis ears, they're just microphones on alligator clips that you attach on various points you suspect. You're welcome to borrow them, im located in Springvale south, not too far from you. Pm me if you want to give them a go.