i'm pretty sure all they do is check the sound level with exhausts.
You mightn't be keen, but you can stick a baffle plate between two flanges to shut it up a little. Mine got through by doing this. If you do use one, just make sure you drive like a granny and try and stay off boost as much as you can.
With the diff, just try and ride the clutch when the car is in the inspection shed, so it doesnt lock and chirp the tyres.