I have a very similar sound, which I can only describe as a top end metalic rattle - only when the engine was cold, and it was worrying me slightly. I took it for a service and mentioned it to look into and they said nothing was wrong, just the normal noise that these engines make when cold.
I'll not 100% convinced as it didn't make the noise when new, but it's on file that I've mentioned it so if anything was to develop later then I can refer them back to the first service -I'm not going to worry about it now and enjoy the car.