There may be a TSB (or more) on this creak, finding many complaints from other A3 owners about similar creaks
https://www.audiworld.com/forums/audi-a3-s3-rs-3-mkii-209/creaking-noise-when-going-over-speed-bumps-2919171/
“what they did was based on TSB 2043424/3 : removed the control arm (per the repair manual) and applied grease to the kidney shaped slits on the control arm bushing. Finally, reinstalled the control arm”