I have a 520d AUC 2009 M sport and its lovely, for a bit of back ground the car is mainly used for very short trips in town, at the weekend it gets a blast down some A roads or a motorway cruise to the coast.
When I first got it it was a tad loud so I went to BMW and they changed the airbox mount the mechanic said as it has lots of short trips try running it on V power.
This made a huge difference as now it's very quite from cold, but not when warm as it is much nosier not rough just louder with a background whirring noise.
I have listened to the timing chain sound on you tube and it's not that. I have driven diesels for 20 years you name it Audi merc pug's so I sure something is wrong but BMW say not.
Also I get around 30 MPG my wife drives it and she don't drive fast . So what do you chaps think? is there another 520 owner in the kent SE London area who could compare?
Please let me know