C4 & C5 with squeezing brakes

Hello people At my C4 Coupé (2006, 22,000 km) and at the C5 of my parents (2006, 28,000 km) squeaking brakes are annoying. I was with my already 2 times in the factory town, there was once something changed, which I was also allowed to pay (+100 €), the second time they were cleaned or dedusted – but that only helped for a short time. The squeaking (both) always occurs when the car is driving very slowly, under 10 km/h, so when braking shortly before stopping. , because for me that sounds like an old truck with 500,000 km and not 2 quite new cars. If someone had a tip on what we can do – in my case it is best before the end of January, because the manufacturer warranty expires (but I will have it extended!) Thank you in advance and with kind regards