Okay ..... I just heard back from the dealership regarding the noise on my 2019 built on April 12th and they said my VCT (variable camshaft timing) is going bad and it will have to be replaced. The part is reportedly on back order until January or February, but I was assured that I am not in danger of doing any damage until it is replaced.
interesting. unless the sound goes with engine speed, that sounds a lot like wastegate rattle (waste gate actuators are visible). mine will make a rattle like that especially on cold start, often gets quiet after (i'm guessing) it's done lighting off the cats.
edit:
@waveslayer, your is the exact sound i'm talking about and mine goes away just like that. might not be waste gates, but when the truck is cold and off, grab the wastegate actuators and rattle them... makes the same noise.
here's an example:
somehow i've always considered it to be related to cat light off, but i'm not sure how wastegates would be utilized in lighting off the cats.
i know my M3 cold start sequence sounds badass as **** instead of rattly.
in addition to the classic cold idle phaser noise (only lasts 3s or 5s or so... just long enough for the oil pressure to come up), and the wastegate rattle, my truck now has a distinctly different warm idle diesel-like rattling sound that i suspect is related to tensioners/chain/phasers, and it very distinctly comes from the front of the engine. it has a very different sound profile. will be taking it to the dealer very soon. could be DI, but i'm thinking not.
for another datapoint on start/stop, my truck is driven in sport mode 100% of the time. it also has its oil changed with mobil1 full synthetic every 5k miles, i check the dipstick every 1kmiles or so, never ran it low.
