I think I solved this problem on my 2021 1500 Elevation. I heard no noise when the truck was new, but with more miles, now I'm at 4k, the noise became more prevalent. To summarize, the problem was worse (most obvious) at slow speeds, when turning, and when the truck was on an angle (ie, the road had some slope). Sounds like something is loose. Have someone shake the bed of your truck side to side to recreate the noise, and visually observe the leaf springs, especially at the leaf spring insert to see if this is the source of your issue, to see if this is the root cause of your issue.
With much help from this thread, I added some roughly 1/4" rubber to the leaf springs, sitting on top of the leaf spring insert. Refer to TSP 19-NA-129 for pictures of the factory leaf spring insert. This TSP notes to install new rear leaf spring inserts. These are thin plastic (I think plastic) used to separate the metal of the leaf springs. In my case, when you shake the truck side to side to recreate the noise, you can see the individual leaf springs moving side to side, and the noise seems to originate from the upper leaf spring rubbing against the insert. Rather than replace the insert, I simply added a piece or rubber on top of the insert.
So far the noise appears to be gone. Whatever material the factory insert is made of doesn't work well with the upper leaf spring that rests against it....resulting in noise when the leaf springs move laterally (ie, rounding a turn on a sloped road surface). At least this appears to the be case once the truck gets some miles on it.