Starter drive is hanging up in the flywheel and not retracting. Usually caused by rust or the drive too tight in the teeth. If the drive doesn't retract, the solenoid stays engaged.
I have the same crap with my 3.0. Either it stays stuck or it won't grab in the flywheel!!! How do you align it properly?????? My flywheel is looking a little rough in the gears! Don't tell me I have to change it?!!!