2001 Pontiac Bonneville Starter

My son borrowed my Bonneville a couple weeks ago and called me saying it was running funny. It turned out to be the fuel pressure regulator. In the process he hadn't noticed the leak in the coolant system and allowed it to overheat for who knows how long. Shortly (within hours) after replacing the regulator and fixing the coolant system the starter appeared to die. When I turned the key all I got was a loud click. So I put a new starter in. I tried to start it and it turned over for about 3 seconds and quit. I get the loud click again. So I got a replacement starter. Same issue though, it turned over for about 3 seconds then stopped and all I get now is the click. All the relays and fuses check out fine. Any ideas? Could it be the flexplate? The battery is practically new. All connections are fine. Thanks for looking.