The noise could be strut mounts - common issue with the S550.
It could also be related to the steering shaft.
It's hard to really know without seeing the car in person. Sometimes even if the owner takes videos, sound is captured different in a video than it is being in or outside of the car.
Sound is coming through the steering wheel. I will have to get it into the air and see.
Thought there might have been a "common" issue that I could look at.