Well, I got a chance to remove the bottom inspection shield off of the transmission and removed the starter today. Starter looks to be just fine. Found where the area around one bolt around the perimeter of the flex plate is cracked, and the ends of some of them look to be cutting a deep groove into starter - evidence of fresh metal particles there, and the arc they are grinding through the starter looks clean and fresh. Cracked flexplate would seem to be my culprit? At higher speeds the cracks are allowing the flex plate to, well, flex too much? (Any advice is much appreciated!) Is this something I'll be able to get new at an auto parts store, or would you suggest I look elsewhere (and if so, where?)? Thanks all.