So when you crank and the engine is running for that quick two seconds, makes a grinding noise? Sounds like that the teeth on the starter motor are'nt springing back away from the flywheel teeth and just grinding against them when the engine is running. Your options are pull it out and take it to a auto elec to have a look at, or buy a second hand or new one. If it was my car i would take the starter to a auto elec.