Go get some rat traps and some peanut butter, smear the peanut butter on the part where you always see people put cheese, set the trap and put it in the closet or wherever they're coming and going from. Repeat until the skittering in the walls is over. If this just happened all of the sudden (as in you haven't had a rat problem for years) it's probably only a couple of rats.
But if you keep waiting around, they are going to multiply the longer you wait the faster they'll multiply and the harder it will be to get rid of them.