2001 Chevy Impala Starter Grinds Intermittently When Engine

Intermittently, the starter grinds when the engine starts. It doesn't happen all the time. And many times, it starts fine without any grinding noise at all. It does seem to be happening more frequently over time however. What is causing the problem? Why is it intermittent? How do I fix the problem permanently? Can the fix be done by a "weekend mechanic" with good mechanical skills and a modestly stocked tool box? Any special tools needed? If battery is disonnected to replace starter (if needed), will the power disconnect cause any car computer programming loses that will require reprogramming? Or, must the repair be done by a professional mechanic or car dealer shop?