The brief
Patrick was annoyed by an unusual noise coming from under his A3, so he checked it in to get it sorted. A noise from underneath that changes with speed usually points at the wheel bearings, and worn bearings don't just drone, left long enough they can let the wheel develop play, so they're worth dealing with. The wheel bearings let the wheels spin freely and carry the weight of the car at each corner. They wear over the years, and when one starts to go it makes a humming or droning noise that rises with speed and changes when you turn. While the car was in, the check also caught the bonnet sitting misaligned because its pneumatic struts had given up, so that got dealt with too. Worn bearings and tired bonnet struts don't recover, so both get replaced.
The diagnosis
On the lift the noise traced to the rear wheel bearings, worn out, which is the unusual sound from underneath that rises with speed. And the bonnet was sitting misaligned because the pneumatic struts that hold it up had lost their gas. The rest of the suspension was sound. That's a rear wheel bearing replacement plus a pair of new bonnet struts, the noise fixed and the bonnet holding properly again.
The work
The worn rear wheel bearings were removed and new genuine Audi-spec bearings fitted, every fastener torqued to the manual figures and the hub nuts renewed. The tired bonnet pneumatic struts were replaced with a new pair so the bonnet stays up and sits aligned. The rest of the rear was checked while it was up. A road test confirmed the noise from underneath gone, the rear quiet and smooth, the bonnet holding up and sitting square, and no warning lights.
The outcome
No noise from underneath, the rear quiet and smooth, the bonnet holding up properly and sitting aligned, and even tyre wear. Patrick got the A3 back quiet again. Worn wheel bearings only get louder and can develop play, so replacing them dealt with the noise, and the new bonnet struts sorted the misalignment in the same visit.