The brief
The owner had been hearing a low hum from the front of the 730Li that built with road speed, plus a faint growl when the front loaded up in a corner. That is the classic wheel-bearing signature, a rumble that rises and falls with speed and changes with cornering load. He brought it in for a proper diagnosis.
A wheel bearing lets the wheel spin freely on the hub while carrying the weight of the car. When it wears, the rollers inside start to chatter, and the noise comes through as a hum that tracks road speed. Left long enough a worn bearing develops play and can eventually seize, so it is not something to keep driving on once it has announced itself.
The diagnosis
On the lift each front wheel was spun by hand and listened to: the bearing on the driver side had clear roughness on rotation, while the other side was still smooth. The hub also had a touch of play when rocked.
There is no greasing or repacking a worn modern wheel bearing, it is a sealed unit, so the fix is a new one. With only one side rough and the other fine, the worn side was the one to do.
The work
The calliper and disc came off, the worn wheel-bearing unit was removed, and a new BMW-spec hub bearing fitted in its place, the axle nut torqued to spec. The hub was reassembled and checked for silent, free rotation by hand before the wheel went back on.
A short road test confirmed the hum and the growl were gone before the car went back to the owner.
The outcome
The hum was gone, the cornering growl with it, and no play at the hub.
The 730Li went home quiet through the front again. For the owner that is a refined car restored, no more rumble building under it at speed, and dealing with the bearing once it started talking meant a planned replacement rather than waiting for it to develop the kind of play that puts a load on the brakes and the steering.