Don't be too hasty, the older N47s suffered with timing chains a lot more than the f30 where i thought this was quite rare?
I'd definitely cease driving it and get a second opinion though from a reputable specialist.
This sounds nothing like yours:
Out of interest, is your car well serviced? I have a 2013 320d SE Manual - I just got it serviced ahead of schedule, my specialist advised that the timing chain even on the older models only affected a small number (Internet makes it feel worse) and that the main culprit is not looking after it.
The oil lubricates the chain (Unless i'm mistaken here) so good quality oil regularly changed will make a world of difference. Same on an old Vectra 2.2i Petrol - Had a 20k service interval to suit fleet owners, the oil got gunky, blocked the injector that sprayed the chain and guess what happens next?
I'm servicing mine annually, approx 10k PA I do.
1st - 19k, 2 years
2nd - 38k, 3 years
3rd - 47k, 4 years
Think that's how mine is at the moment, I will be servicing it next year at approx 57k too.