The brief
The 528i had developed a light rubbing or knocking from the front when it crossed humps and uneven roads, the kind of noise that gets on your nerves and tells you something up front has gone slack. He brought it in. That points at the front shock absorbers, the struts on the front of these. The strut damps the spring, it stops the car carrying on bouncing after a bump and keeps the tyre planted, and the top mount that bolts it to the body has a bearing and a rubber cushion built in. As the strut wears, the damping fades and the body floats, and as the mount perishes you get knocking and rubbing over bumps as the strut moves against a worn cushion. A worn strut and a tired mount only get worse, so they need changing.
The diagnosis
On the lift each front strut got a bounce-and-inspect. Both were past it, weak damping, weeping, and the top mounts perished, which is where the knock was coming from as the strut worked against worn rubber. The rears were still doing their job. When the pair on an axle have gone together, you do them as a set with fresh top mounts, a new strut next to a tired one gives you a car that handles differently side to side, so the call was both fronts.
The work
Both front struts were unbolted and removed, and a new genuine BMW-spec pair fitted with fresh top mounts and bearings, every fastener torqued to the manual figures. With both sides back together the front geometry was checked and set so the new struts weren't fighting a misaligned corner. A road test confirmed the knock was gone, the ride had settled, and the front was planted again over bumps.
The outcome
No more knocking over bumps, a composed ride that settles in one motion, flat through corners, and the front planted again. The 528i went home with the front end quiet and tight. Worn struts and perished mounts only get noisier and softer, so doing the pair as a set with fresh mounts reset the front end rather than leaving one side lagging the other.