Polytek'd the rear diff mount the other day (70shore). Its made a huge improvement! However, it has also made the car make an humming / whining noise from the rear at speeds over 70. It only happens when on the throttle, as soon as you back off it stops. I need to have an have a proper play with someone in the back to listen, but I think its from the right rear, and didnt seem to be effected by turning (although it was only sweeping motorway type bends).
I suspect its always had this issue, its just that only now is it audible.
The car has always suffered from drive line take-up when slow speed maneuvering / reversing and sometimes when accelerating hard for a period then backing off - although this does seem to have almost gone. This slack remains with the polytek'd diff mount but is more of a mechanical clunk now than a dull thud.
How can I work out of its the diff / diff bearings / CV joints (and which ones) / wheel bearing (maybe the whining is un related to the drive line slack?).
Help please! the drive line slack wasnt really a problem and may be unrelated, but the whining noise will make me go mad!
Note, the car has new RS4 snub mount, lemforder gearbox mounts, and 034 motorsport road spec rear diff mounts. The drive line slack noise is deffinitely from the rear drive train.