That sound is mild, my 328i with the same engine sometimes makes that noise. Sounds like marble in rattle can almost. Under warranty I had bmw replace lifters which helped for a little bit but it came back. Usually cold days but has happened in warmer weather too. Eventually the sound goes away.
There is an additive for noisy lifters you can use. I've tried to buy it in the past but its always out of stock in canada.
https://www.ecstuning.com/b-liqui_mo...0ml/20004~liq/