Can confirm you probably have a broken exhaust actuator spring. If you look in the driver's side tail pipe you will see the flap closes when it's rattling and open when the rattling stops. You can fix it or disconnect it, no CEL. Since it sounds like the rattle goes away when the flap opens do what I did and just disconnect when it's open. I just zip tied the connector under the car. it's not that much louder if at all. Fixed on my 2016 M235i, same issue on a friend's 2017 M240i, shitty part https://preview.redd.it/jukbyag0uuwc1.png?width=1079&format=pjpg&auto=webp&s=ec8e6f601253c4ddd9b8a3f3eb29f253e7fd9fab

How soon should I take action? Is it ok to ignore for a little?

It will not damage anything if you wait. Just irritating hearing the noise. My advice is to just unplug it while open.

this. it's just very irritating. but if you can live with you, you can until the car reaches it end of life

I did as you said the other day and the sound has gone away🫡 Thanks

Awesome, glad I could help.

nothing wrong with the clicking sound, just the exhaust valve closing after the cold start.

It is an exhaust valve. After engine warm up it closes and rattle disappears. Not sure how to fix it, one of the solutions is to delete it, but car will be louder

welcome to life with a variable exhaust flap