Why is a grease like substance filling my starter, causing intermittent starting?

I have noticed a humming/grinding noise coming from drivers side of engine, near where flywheel is located. Noise gets Louder when turning, or at lower speeds. I need to know what might cause this noise, and where this grease is coming from. I'm considering pulling out the flywheel, but could the grease be coming from my transmission? Its a gray, or translucent black grease. Maybe Flywheel is grinding on something? Maybe Ball bearing Grease from a joint? Any suggestions would be appreciated.