Creaking when steering (Handbrake applied)

[Lawrence25]

Just got myself a used Honda Civic 2015 1.8 Ivtech and I've noticed a really annoying creaking sound at the back of the car.

The garage had a look at it and said it was aluminium corrosion build up between caliper and rubber for slide.

However, It's still there! What else could it be? It seems to only happen when brake is applied.