The brief
The 320i had a loud knocking sound whenever it crossed a hump, with a choppy ride to go with it. The knock over humps usually means the shock absorbers and their top mounts. He brought it in. The shock 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 shock wears the damping fades and the body floats, and as the top mount perishes you get the knock over humps as the strut moves against worn rubber. A worn shock and a tired mount only get worse, so they need changing, the matching corners together.
The diagnosis
On the lift each shock got a bounce-and-inspect. The fronts and rears were past it, weak damping, weeping, the body carrying on after a push, and the top mounts perished, which is where the knock was coming from as the strut worked against worn rubber. The shocks had all done their miles. When they've gone like that, you do them as axle sets with fresh top mounts, so it was the front pair and the rear pair, fresh shocks and mounts all round.
The work
Both front struts and both rear shocks were unbolted and removed, and new genuine BMW-spec shocks fitted front and rear with fresh top mounts and bearings, every fastener torqued to the manual figures. With everything back together the front geometry was checked and set so the new shocks weren't fighting a misaligned corner. A road test confirmed the knock over humps was gone, the ride had settled, the car planted again.
The outcome
No more knock over humps, a composed ride that settles in one motion, flat and stable through corners, and the tyres back to wearing evenly. The 320i went home riding properly again. Worn shocks and perished mounts only get noisier and softer, so doing the lot as axle sets with fresh mounts reset the car rather than chasing the next worn one a few months later.
