Why is a new starter still grinding?

This is probably 100% because the teeth on your flywheel are worn out from trying to start it with a bad starter too many times. I had this same problem, changed my starter, it worked like twice then started grinding again. Took it out and look at the flywheel and it was toast. Changed the flywheel the worked fine. Had to replace the started again 8 months later because, well, thanks O'Reilly!

Replacement of a flywheel can run you from $500 to $1000+ for a mechanic. Its about $180 for materials (w/ clutch replacement as well, I mean since you're RIGHT THERE). Need a second person though because taking that tranny out is a beeyotch. If your car is new, it won't be SOO bad. The bolts on my truck were rusted so it took about three days.