Are you certain it is transmission vibration, caused by rotating parts, and not simply some of the new plastic panel work, ie under body panels that are vibrating, and reach their natural resonance.
The fact it is happening on so many, means that there must be something in common.
Are they all 4x4, same engine, same options, same trim,? there must be a common factor, especially if you can eliminate some that don't do it
I once had the under body panel of a 4x4 vibrating, it sounded like a machine gun, luckily the vibration also happened at a fast tick over, so it was easy to find, I just tightened one M6 bolt. Sorted.
With modern cars, they seem to opt for plastic rivets, quick and cheap assembly I guess, which hold a panel secure, but cannot be tightened up later.
There could also be a heat shield that has been knocked or is touching the exhaust, or body, or is loose, or missing a clip.
I hate vibrations and rattles.
Our Picasso had an annoying rattle, and simply it was the rear seat belt, that after use, settled touching the rear door panel. So stop the car, jam the clip in the upper holder and it was fine until another passenger had been in the back...
We travelled up to Aberdeen for Christmas in our brand new yeti, and what we did notice was there was a lot more road noise on their motorways than on say the M6 , given the same speed, 60-70 mph
The hard shoulders on many motorways was often covered in loose gravel, which might in part be due to debris from the main carriageway breaking up and resting on there. The road surface was certainly rougher, with larger spaces in the surface, thus increasing the noise, and I guess subsequent vibration.