2018 Silverado here. Over the winter I noticed a prominent rattling coming from somewhere underneath the vehicle that was made worse whenever I am stopped but in drive. For example, its the absolute loudest/worst when I'm going through a drive-thru and having to move forward and stop, move forward and stop, etc.
Finally I noticed I could hear it rattle momentarily even when the truck is completely off and someone slams one of the doors hard.
I went under the vehicle this morning and poked/prodded around and seemed to have found the spot where the rattling noise is coming from. Its either the muffler or a part of the exhaust:
I uploaded this YouTube video which shows the rattling happen when I bang on this part with my fist.
Anybody have any idea(s) as to what could be making this noise, and what the fix is?