Apologies for weird typos, my Android phn app for this site is a bit funky and my autocorrect needs to take an ESL course....
There is a YouTube video you can search for, I'll post it if I find it again later, guy mounted a camera to undercarriage because he's got one of the mystery noises. I didn't hear my noise in the video, but you can see lots of stuff vibrates jangles around going dwn road.
Crambo I think you are right about lugging and my rattle. I have 3:42 gears and drive rural mountains. I also often lockout over drive untill im at high cryisung steady speed. The overdrive on the auto trans feels to me much more like the OD on a manual transmission, it just has that feeling of being a higher speed, highway, cruising gear. My rattle sound is quite a bit like when I've had a manual trans and you shift wrong, lugs a min and things rattle for a second. But the vehicle doesn't shudder at all.....it sound kinda like if you lug a manual for a sec and you have loose heat shield on the exhaust and that rattles for a sec.
There seem to be a lot of posts on various forums related to the trans shifts and the " what's this noise?" Stuff. The trans has a different kind of feel to it than other older auto trans. I think it adapts to me and I also adapt to it. It just behaves like...to me the feel is much more like a manual trans if that makes any sense at all. Other automatics I've had kinda just do their thing and you don't have much input, this one, you can kinda make it shift more intentionally with how you use the pedal without " getting on the pedal"..... I don't know if this makes any sense it's just how the animal feels to me! Im a horse trainer so perhaps I tune in to such things! The 2014 is definitely a nifty animal but it's got some quirks, not necessarily bad, just different feel to it.