The brief
The A4 had developed clunking and knocking from the suspension over bumps, the steering had gone loose and imprecise, there was a vibration through the wheel at higher speeds, and the front tyres were wearing unevenly. Those are the signs of worn upper control arms. The front upper arms work with the lower arms to locate the top of each front wheel and hold it at the angles the geometry is set to, pivoting on rubber bushes and ball joints. When those wear, the wheel can move around more than it should at the top, which is the clunk over bumps, the loose, vague steering, the vibration at speed, and uneven tyre wear because the wheels aren't sitting where they're aimed. Worn upper arms only get worse, and they take the steering precision and the tyres down with them.
The diagnosis
A pry-test on both front upper arms confirmed it: the bushes were deflecting past the service limit and the ball joints had play, with the rubber cracked, on both sides. One arm was no better than the other. When both are tired together you do them as a pair, fitting one fresh arm against a worn one leaves a mismatch front to front, so it was both, with a four-wheel alignment after to reset the geometry on the new parts.
The work
Both front upper arms came off, and a matched pair of genuine Audi-spec replacements went on with new bushes and ball joints, every fastener torqued to the manual figures. Then the car went onto the alignment rig for a four-wheel set-up. A road test confirmed the clunk was gone, the steering had tightened up, and the vibration at speed was gone.
The outcome
No clunk over bumps, precise steering again, no vibration at speed, and the alignment back on spec, so the front tyres will wear evenly. The A4 went home tracking properly. Upper arms carry the front geometry along with the lowers, and once their bushes and joints wear the steering and the tyres pay for it, so a fresh matched pair and a reset alignment put it all back where it belongs.