The brief
The Q3's steering had gone unstable, hard to keep straight and pulling to one side, with clunks from the front over bumps and turning, and the front tyres wearing unevenly on the edges. 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 bushes crack and the joints develop play, the wheel can move around more than it should, which is the wandering steering and the pull, the clunk over bumps, and uneven tyre wear because the wheels aren't sitting where they're aimed. Worn lower arms only get worse, and they take the handling and the tyres down with them.
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 stiffness 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 steering had firmed up, the pull was gone, and the clunk over bumps was gone.
The outcome
Stable steering, no pull, no clunk over bumps, 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 drifts and the tyres pay for it, so a fresh matched pair and a reset alignment put it all back where it belongs.