When I had a new diff fitted under warranty, it made the usual groaning noises. I wasn't too fussed as I expected it, but given that it was pretty loud at low speeds on tight manoeuvring, the master tech decided it was best to change to the SAF-XJ +FM booster (83 22 2 282 583). FM being a fluorite based friction modifier. The noise disappeared.
I was initially hesitant about having the FM in my diff fluid as I believed that the FM would delay diff clutch engagement, but the tech assured me that there won't be a performance difference, which was proved by a track day soon after. I still managed to get power down very early on the outside rear wheel when powering out of a corner.
Last edited by mlhj83; 06-28-2012 at 12:38 PM.