Synopsis: Brought vehicle into dealer for rattling sound in rear of vehicle.
Repair: Installed clips to repair a dangling wire for the parking brake

Issue today: Reversed out of garage, disengaged parking brake, and massive squeal

Confirmed actions:

1)Sound remains when vehicle is in neutral rolling down a hill.
2) Sound remains while vehicle is in motion while neutral and applying slight brake.
3) Sound changes if I apply parking brake. (sound becomes louder, same type of scraping sound)

Suspected issue: Parking brake isn't fully 'releasing'

If I slam on the parking brake FULL/HARD while the vehicle is moving, and disengage it, the sound goes away. If I press the parking brake a few notches so it partially engages it, and then I release it, sometimes the sound comes back. When it does come back, it varies from a slight "hum"..."hum...."hum".... to a "scratch"..."scratch"..."scratch"....or if it doesn't come back, I hear nothing at all it and it appears to just go away.

Here's the interesting bit

After I messed around with the parking brake for a solid 20 minutes of testing (for the above), the issue is now "gone". [wtf?]

What should I do now? When I leave the vehicle in neutral with the parking brake disengaged and I jack up the wheel in the back which I think has the parking brake problems, I can't turn the wheel either (I suspect due to 4matic).

What should I do next?

This video is taken when the issue first started, before my testing and effing around of the parking brake.

Thanks!

http://sendvid.com/7za3d83y