Currently have a 2020 AMG GT, I've taken the car to the dealer several times however they were not able to replicate the sound. The sound is mechanical and is coming from the rear of the car when the car is both moving and fully stopped. It happens in comfort, sport plus, manual and in automatic.

 

Wanted to bump this for you. I have no clue what that noise is. Very weird!

Lots of knowledgeable people on this forum, hopefully someone can help you.

 

To me, it sounds like a hydraulic pump starving for oil