Well damn!
This starter I just installed has died. Turn the key and there is nothing more than just a single click coming from the solenoid. Started up a couple of times just fine prior to that. Actually have the car on the lift, so that is lucky. I found that I could recreate that drivetrain noise with the car off of the tires and the emergency brake engaged, so I was going to have Connie help me with this. I showed her how to feather the clutch while in gear to make the noise happen (which even now was still intermittent), and then raised the lift so I could get underneath with the camcorder to try to identify exactly where the noise is coming from.
So while Connie was getting used to the clutch engagement, she stalled the engine. When she tried to start the car again, nothing but the solenoid click mentioned above. So I got into the cockpit and tried myself. Took the emergency brake off, made sure the rear wheels would turn when the transmission is out of gear, etc., and it appears to definitely be the starter.
I contacted RockAuto to see if they will do anything about this. I was gone on vacation the entire month of May, so that starter doesn't have any more than maybe a dozen or so startups on it. But their 30 day guarantee is long gone, of course. So we'll see what they say.
I have to admit I was a bit concerned that the starter I got did NOT say "ACDELCO" on it like the one I removed. I think if I have to buy another one, I'm going to insist on seeing that on the one I get.
Well, at least this didn't happen while the car was out somewhere meaning I would have to get it towed. But still............ So much for buying what is supposed to be a good brand name item.