Help 2015 120d xdrive whistling under acceleration

[Jackdyo]

Hi all,

Need help my car is currently making an awful whistling sound under acceleration, I can cross the following of my list Turbo (fitted brand new 2 months ago was thought to be original cause for noise) rear diff (new rear diff fitted 1 month ago had leaked and bone dry)

I've had the car 6 months now and noticed the noise around 4 months after getting the car, recently it's become louder and more constant when accelerating

I have so noticed a major decrease in MPG and the car is not as responsive or quick as when I got it

Tbh it's driving me mad and hoping for some input