The brief
The Golf had a hum at motorway speed that the owner had narrowed down by ear to the back-left of the cabin. He'd noticed it was clearly louder turning right, which loads up the left rear, than turning left. That listen-and-load test is the classic way of pinning a noise to a particular wheel bearing.
A wheel bearing lets the wheel spin freely while taking the weight of the car at that corner. As it wears, the rolling surfaces roughen, and that's the hum, which rises with speed and changes with cornering load because that's what changes how hard the bearing is working. A rear bearing making that noise has run its course.
The diagnosis
On the lift the workshop spun each rear wheel by hand and rocked it top and bottom. The affected rear bearing had clear gritty resistance and a small amount of play at the hub, the play you don't want. The other side felt smooth.
With both rear bearings the same age and one already worn, the call was to do the pair rather than leave the second to start humming a few months later, so both rear hub bearing assemblies were getting changed.
The work
The brake calliper and disc came off each side, the old hub bearing assemblies were unbolted and lifted away, and new VAG-spec hub bearing units bolted on in their place. The axle bolts were torqued to spec, the brakes reassembled, and each hub turned by hand to confirm it ran smooth and silent before the wheels went back on.
A road test confirmed the hum was gone, no growl in the corners, and no play at the hubs.
The outcome
Hum gone, no growl through corners, and no play at the hubs.
The Golf went home quiet at the back again. A wheel bearing gives you a good warning before it lets go, so acting on the hum and doing the pair while it was in meant a clean job rather than a return visit for the other side.