I have a 2002 Ford Explorer. It had loud rear gear noise when I purchased it several years ago. I took it to the Ford dealer. The service manager said that he owned the same year and model and that it is just how they are going to sound...that he could fix it but that the gear noise would come back. I took it to a driveline shop and they rebuilt the unit and the sound was 99% gone. Now I'm hearing some moderate gear noise again from time to time. Sometimes it goes away. It is more pronounced when driving on windy roads. I understand that many late model Ford limited slip differentials have this problem. I'm wondering if anyone has found a solution using Amsoil or Redline or some other high end fluid. I have been having Ford change it every year or so at high cost, which includes their factory synthetic fluid and friction modifier. I had Jiffy lube do it once, but there didn't seem to be any difference. Amsoil says that their fluid doesn't need friction modifier, but that they have one in the case it is needed?! That seemed strange, but I'm thinking I need it all, if a fluid would make a difference. Anyone have experience with this?