The grinding sounds like the starter motor drive gear is hitting the flywheel teeth, engine
running. Taking the negative battery cable loose should stop it, taking the cable loose might
cause other issues? Check applicable trouble codes, relating to starter. you may have to
check manufacturer specific codes as well as po codes. Two voltage circuits at starter
motor, one is hot all the time. The other goes hot with key in the crank position. Check that
wire for voltage, key off, should not be hot. You can use a test light. If it is hot, either
shorted to voltage or the integrated power module thinks your trying to crank the engine. If
it isn't hot and starter motor still kicking out drive gear, I think something wrong with starter
motor. Just my opinion.