ok, something's up. contact apple. meanwhile...that's five, out of...how many early 2015 rMBPs are out there? call. apple.
There are many stories about, that they changed the LCD 2-3 times and the rattle is still there.
I have since ordered 2 more Macbook Pro's and 1 of them has the issue again. This is 2/3 Laptops with the problem.
This is the second of three Macbooks we have purchased which has loose parts inside.
In the video of the first Macbook you can hear the noise clearer. This is recorded with my phone so the sound is not as good"
and..
just read the comments, everyone has the same issue