I wanted to provide some input on this because even my 2017 Z with less than 10K miles started to have the infamous window rattle. I was able to narrow it down to what appears to be a device that keeps tension on the cable used to drive the window up and down. It a spring loaded device with a 2 piece toothed ratchet mechanism.

When the window is moved upward, slack is created in the cable at the tensioner location and the spring keeps tension on the cable. When the window is moved downward the ratchet engages and allows precise movement of the window without letting the spring compress.

When the window is rolled all the way up pressure is removed from the ratchet gear and since it is free floating in there its loose and starts to rattle. I think this is more pronounced as the cable stretches which may be why a new regulator doesn't rattle but not long after will start to rattle. As soon as you start to move the window back down the ratchet re-engages and the noise goes away.

I ended up removing the ratchet piece of the gear entirely to get rid of the rattle. Alternatively you might be able to pack the inside of the mechanism with a thick grease to prevent the gear from rattling. Removing the ratchet in theory would make the down movement of the window less precise since the first initial movement of the regulator motor would be used to compress the spring, but I haven't seen any noticeable difference and the window still moves down and out of the way quickly when opening the door.

Its easy to take the tensioner apart, simply compress the spring and then undo the cable from the pulley marked with the green arrow. Once the tension is relieved from the cable the tensioner will come apart and you can remove the gear piece or coat it with heavy grease.

You will of course need to remove the glass and the regulator assembly to get to this since its behind the big metal panel in the door.

Hopefully this is helpful for someone. If anyone else can figure out a better way to prevent the free floating ratchet from rattling please chime in.

If only you had taken a video of this process��. I am having what seems to be the same issue. Something will rattle under brass produced by the car’s speakers, and it ONLY happens when the window is all the way up. My issue is that I have no idea how to remove the window, and I am nervous I would mess something up if I attempted it.

Has anyone tried packing the mechanism with grease?

I can confirm that packing the mechanisms with bearing grease works to stop the rattle, will see if the noise comes back in time but so far so good!

Fixing the rattle
 

Nice! Since that is just a temporary fix, I made a full DIY on how to remove the gear in case you were interested. Here is the link to the unlisted video. https://youtu.be/aTeq8NIkjZ8