The brief
The Q3 had uneven tyre wear, clunking and knocking over bumps, poor handling and instability, a vibration through the steering wheel, and the alignment was off. Those are the signs of worn front lower arms. The front lower arms locate the bottom of each front wheel and hold it at the angles the geometry is set to, pivoting on rubber bushes and a ball joint. When those wear, the wheel can move around more than it should, which is the clunk over bumps, the vibration, the loose handling, and uneven tyre wear because the wheels aren't sitting where they're aimed. A worn lower arm only gets worse, taking the stability and the tyres down with it, so it needs changing rather than chasing alignment that won't stay set.
The diagnosis
A pry-test on both front lower arms confirmed it: the bushes were deflecting past the service limit and the ball joints had play, with visible cracking in the rubber, 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 lower 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 handling had tightened up, and the steering vibration was gone.
The outcome
No clunk over bumps, stable handling, no steering vibration, and the alignment back on spec, so the front tyres will wear evenly. The Q3 went home tracking properly. Lower arms carry the front geometry, and once their bushes and joints wear the handling and the tyres pay for it, so a fresh matched pair and a reset alignment put it all back where it belongs.