I'm wondering if the park brake is on and the steering is out of neutral. Its trying to move but can't, it causes a grinding sound and will stall the engine too.It is pretty hard to troubleshoot a grinding noise with out being there , couple of things I would do from what you are saying would be to remove the drive belt and start the motor with out the pump turning , that would eliminate the pump , you could remove the hydraulic filter and case drain filter and check for signs of failure , cut the filter open with a sawsall or grinder if metal doesn't just pour out of it with the oil