Every So Often I Have A Very Loose Movement After

Every so often I have a very loose movement after a normal evacuation. It is an uncontrolled bowel movement. It comes on so quickly I can barely make it to a bathroom, and sometimes I cant make it if I am outside. Usually it is a second movement after a normal evacuation. Very disturbing since I dont know what brings it on except I can feel cramps or a rumbling in my belly before an attack.