2004 shaky S500

[Boston Benz]

I was wondering if someone could help me with this one... My friend has a 2004 S500 with 130K miles. His car/engine shakes at anything over 1,500 rpm. You can even feel it in the floor. Anything below 1,500 rpm - smooth. That's at park if you were to increase the rpms or while driving, both the same result. With the hood open and the rpms at or above 1,500 rpms, the engine is completely still so I have to rule out motor mounts. Any ideas?