Rattle on cold start for two seconds, 2016 520d F10, worried about the chain

2016 520d F10, 74,000 km, bought second hand last year at 61,000 km with full history.

On the first start of the day, and only then, there is a rattle from the back of the engine that lasts about two seconds and then goes completely. It does not come back on a warm restart. Nothing on the dash, no smoke, oil level steady between changes, and the car drives properly otherwise.

I know what this engine is known for and the rattle being at the back of the block is exactly what has me worried. My understanding is that later builds got a revised chain, and I am not certain which side of that change a 2016 car falls on.

Before I start pulling things apart

1. If you have had the chain done on a 520d, what were the early signs and what did the job cost you
2. Does a two second cold rattle on its own justify opening it up, or is that still in the wait and watch zone
3. Is there a way to tell from the VIN which chain is in there

I use 5W-30 to spec and change at 10,000 km rather than the longer interval the car asks for. Independent specialist in Delhi NCR who has done this job, recommendations welcome.