I recently had a new 9" fitted to my HQ - LSD, 3.25 ratio - and it is very noisy. The noise it produces is a whine from about 60/70kph through to about 100kph. It does it under acceleration of any level and also under a trailing throttle. On a neutral throttle it is silent. I have had the centre removed and returned to the mob I bought it off in Melbourne, who said they could find no problem with it, but fitted a different brand of gears anyway and returned it (I think originally they had Ford gears in it and replaced them with Motive Gear, but I may be wrong). The diff still whines - the noise seems to be at a different 'pitch' but occurs under the same circumstances. I've spoken to the guys that built the diff and they suggested it is not a problem with the diff, but rather something else. They suggested that the pinion angle in HQ's is marginal and that that can produce the noise. Now, while I'm no expert, it had a 9" open diff with the same gearing in previously and it was silent. The mob suggested I fit a set of those udjustable upper and lower trailing arms to my rear suspension to adjust the pinion angle. I've had people suggest it could be wheel bearings or the transmission - I'm in the process of checking all of these but they didn't make any noise previously.

Anyone have any advise on the subject?

Cheers for any help.