I will provide an honest answer. I trust this will be appreciated. Please remember that a low rating PUNISHES me for being honest and that I receive nothing for my time until a positive rating is clicked.
as I am sure you can appreciate, it is difficult to diagnose a noise that one cannot hear, but I will do my best to provide helpful info
my assessment based on your description is that this is most likely nothing to be concerned about if it goes away once warm. usually a tapping noise is just the valve lifters being noisy which has no impact on longevity or performance.
if you are very worried, it would be worthwhile to have the vehicle inspected by a trained BMW technician who is familiar with this engine to make sure it is nothing more serious
Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle