I would start by getting the tires and wheels high speed balanced, not just balanced regularily.
If that doesn't help, I would take the car to a good independent mercedes mechanic and have them diagnose and check the suspension and related components.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.