Brake problem

Hi all,
i picked up my car today finally, and i absolutely love it.
But, there is a random sqeel coming from the rear brakes when you cruise along, then when you touch the brake pedal it stops. Has anyone come accross that before? It spoils the ride this thing and i would like to get it sorted.

The rear calipers have stuck on the sliders.
Common problem, they should be stripped, cleaned & greased at service time, but most probably are not.