Brakes locked

Car has been parked up over the weekend. When I took the handbrake off this morning and reversed what a noise it made. Sounded like a clunk thinking brake pads but will wait to see if you have suggestions. Weather conditions.... Damp but not freezing, has been very windy.

Pads rusted to the discs, as the handbrake uses the rear brake pads onto the disc surface, and not the old system of separate shoes in a bell (which still used to stick a bit).

I always leave my car in gear with the handbrake off, over night, yet it still does it sometimes after a weekend of not being moved.

Thanks Araf.

Mine did it on Monday yesterday having not driven it since Friday in the rain. It happens quite regularly