Not been exposed to a car that's had a dodgy diff so I wondered what the symptoms were? (4x4 saph)
The car is driving great and properly fast so I'm happy, but last night I noticed when slowing down that there's a droaning kind of noise coming from somewhere, it seems to be a lot more prevelant when off throttle but the exhaust note is very loud inside the car when driving so I cannot say for sure it's not there all the time.

I've had wheel bearings go out on me before and checked these very recently, it doesn't sound like a wheel bearing type of noise. Loving the T4 power but it's definately testing the rest of the car!