The brief
The A3 had developed a hum from the front. It started subtle, the kind of noise you only notice on a quiet road, and over time it grew into a definite growl at higher speeds.
Two other things came with it. A vibration through the steering wheel. And the noise changing pitch and volume when the owner turned, getting louder on one direction of turn than the other.
That last detail is the giveaway. A wheel bearing carries the car's weight as the wheel spins, and when you turn, the load shifts from one side of the car to the other. A worn bearing that is being unloaded goes quieter; one being loaded up gets louder. So the noise changing with the direction of turn tells you which side has the bad bearing.
Classic wheel-bearing pattern, and a clear one.
The diagnosis
Up on the lift, the simplest test first: spin each front wheel by hand and feel for it.
The affected side had clear gritty resistance, the feeling of a bearing whose rollers and races have started to wear and pit. There was also a small amount of axial play at the hub, meaning the bearing had developed a little side-to-side slop it should not have.
The other side spun smooth and silent with no play, which confirmed this was a single-bearing fault, not both sides ageing together.
A worn wheel bearing only gets worse, and a bearing that fails completely can lock a wheel or let the hub move enough to affect steering and braking. So this is one you fix when you find it, not one you watch. Bearing replacement on the affected side.
The work
The brake calliper came off first, then the disc, to clear access to the hub.
We pressed the failed wheel bearing out of the hub carrier. Pressing a bearing in and out is a job that wants the right tooling and the right pressure, because forcing it the wrong way damages the new bearing before it ever turns a revolution.
A new Audi-spec bearing went in, set to the correct preload. Preload matters: too loose and the bearing knocks and wears fast, too tight and it runs hot and seizes. The factory figure is the factory figure.
Hub reassembled, axle nut torqued to spec, disc and calliper back on. Then we spun the wheel by hand again to confirm it turned silently and smoothly with no play, before the road test.
The outcome
The hum was gone. No growl at speed, no vibration through the steering wheel, no play at the hub when checked by hand.
A road test at a range of speeds confirmed the front of the car was quiet again, with no return of the noise on either direction of turn.
For the owner, the practical win is a quiet, smooth front end again, and a bearing that should now go the distance. A worn bearing left to run eventually takes the hub or the CV joint with it, so catching it at the hum-and-growl stage kept the repair to just the bearing.