N47 engine, so all 2 litre diesels I believe. One of the most common bmw engines.
Unfortunately I have a 320 d touring. Chain and guards have already been replaced, under warranty, with the previous owner (father in law). However, there is no certain fix and looking online the issue can occur almost at any stage of the car's life. Annoying as the engine is otherwise great and the car drives well.
Replacement cost for the part is circa £4 to £5 k or something crazy. My car had only done 6k miles when problem was identified. It has now done circa 15k and my father in law recons he can hear the sound again. Annoying as the car is only 18 months old and the most expensive set of wheels I have ever bought.
Car currently broken down with BMW dealer, alternator fried. I had already been in twice to the garage to point out the warning light for the battery was on and explained the handbook said this was an alternator issue...they just charged up the battery when I took the car in.
Sorry for going off topic, but personally I wouldn't get another, despite it being a nice car otherwise.