The brief
Alex's Golf gave a loud thud from the back every time he went over a road hump. He brought it in. A thud over bumps means the rear shocks have stopped damping, and worn shocks don't just make noise, they let the back of the car bounce, which lengthens braking, upsets the handling, and wears the tyres unevenly. The rear shock absorbers control how the springs settle after a bump, soaking up the energy so the car doesn't keep bouncing. Over the years the seals wear and the damping fluid bleeds past, so the shock goes soft and the wheel crashes through its travel and hits the bump stop, which is the thud. A shock that's worn out can't be revived, and they wear at the same rate left and right, so they get changed as a pair.
The diagnosis
On the lift the rear suspension got a proper check. Both rear shock absorbers were worn, soft with signs of seepage, letting the rear bottom out on bumps, which is the thud. The springs and the rest of the rear were sound, and the top mounts were due alongside the shocks. When the rear shocks are gone you do them as a pair with fresh top mounts, fitting one new shock against a worn one just leaves the car lopsided, so the call was both sides with new mounts.
The work
Both rear shock absorbers came off and new genuine VW-spec shocks went on with fresh top mounts, every fastener torqued to the manual figures and the suspension bolts done up at ride height so the new units sit right. The springs were checked for cracks while it was apart and the bushes given a look. A road test confirmed the thud was gone, the rear settled in one motion over bumps, and the car sat level.
The outcome
No thud over humps, the rear soaking up bumps in one clean motion, the car sitting level, even tyre contact, and braking that stays composed. The Golf went home riding the way it should. Worn shocks only get noisier and harder on the tyres and brakes, so doing both rears with fresh mounts reset the back end in one go.