Today my starter engaged and didnt disengage. I heard an awful racket after I started my truck so I got out and opened the hood. Sounded like the starter didnt retract and is dragging on the flywheel so I shut off the key. Well even with the key off the starter is cranking away very rapidly. truck wont start cause the ignition switch is killed. It continued for about 10 seconds. With all the cars ive had and all the problems ive seen this is a new one to me. What would cause it the starter to crank with the ignition on and also off?