The brief
Our regular customer brought his E200 in complaining of a steering wheel that felt loose and vibrated, and a grinding noise when driving. He brought it in promptly, which is the right call, that combination affects how the car handles and it's a safety issue if it's left. Those symptoms point at the front wheel bearings. The wheel bearing lets the wheel spin freely on its hub while carrying the car's weight and the cornering loads. It's a sealed unit, and over the miles the bearing wears, the rollers and races pit, and it gets rough and noisy, the grinding, and once it's worn enough it develops play, which feeds vibration and looseness up through the steering. A worn bearing only gets rougher, and a badly worn one can damage the hub and the brakes, so it needs replacing.
The diagnosis
On the lift the front wheels got spun and rocked by hand. The front bearings were rough turning and had play, exactly what makes the grinding and the loose, vibrating steering, and with both fronts tired from the same mileage. The rest of the front suspension and the steering checked out. When the front bearings have gone together, you do the pair, so the call was both front wheel bearings, sealed units pressed and torqued to spec.
The work
Both front corners were stripped down, the worn wheel bearings pressed out, and new genuine Mercedes-spec bearings fitted, everything cleaned up and reassembled with the hub nuts and the suspension fasteners torqued to the manual figures. The wheels were refitted and spun to confirm they turned free and silent. A road test confirmed the grinding was gone, the steering tight and steady, no vibration.
The outcome
Tight, steady steering, no vibration through the wheel, no grinding, and the front end quiet again. The E200 went home with the bearings sorted. Worn wheel bearings only get rougher and can take the hub and brakes with them if they're left, so doing the front pair put the steering and the safety back where they should be.