Well I have a whirring issue too. But mine is from the rear of the car. The sound gets real loud at about 80 Kph and then sort of dies away as I go fast, but that might be due to road/wind noise over powering it. The noise is there at slow speeds but doesn't really start getting bad until the car gets faster. I am guessing this may be a bearing problem, as there seem to be minimal resistance when the car is rolling in neutral, just heaps of noise. My mechanic says that its the tyres, but I am sure tyres aren't making all the noise, as I would probably hear the same from the front. Now this is a question hard to explain: When the car is jacked up off the wheels, is the rear axle meant to turn as easy as the front axle ? I mean when you turn one of the driving wheels, the Differential function causes the wheel on the other end of the axle to rotate in the opposite direction. With the Front axle I can free spin this up, its nice and easy to turn, however, with the rear axle its like I almost need a crow bar to even turn the wheels, I get the differential effect, but the resistance is so high It feels like I forgot to take the handbrake off... Is this normal for AYC diffs, or is mine stuffed ?