Help!! Liftgate motor has gone wack

[sam123]

I'm not sure if this goes in here or Exerior but my son recorded the liftgate going whack today. I noticed some noise back there while driving and I didn't know what it was but now I do. We've tried to troubleshoot and found that it goes whack when you press the unlock button on the fob or go around the back with the fob on you... we honestly have no clue what could be causing it....

Here's a video of it
https://www.dropbox.com/s/p66yg05ro2qgtxv/IMG_1558.MOV?dl=0