The rust running down the sides will be rust deposits carried by water leaving traces on the side walls.
Rust comes from ferrous metal - might be steel screws rusting over time - may be worth inspecting upwards to find the source of the staining.
If screws replace with Galvanised ones or even Stainless Steel. Wash and scrub the stains away.
Good luck...
Peccavi, February 2010
