I just bought a craigslist sale (Scapin, images posted in this thread).
When I bought the bike, I wiggled and jiggled the headset and BB, and rode it around a little in the parking lot. It had almost no air in the tires and I didn't bring a pump, so it was hard to give it a go. Everything seemed fine, though.
This morning I took it out for a rip and discovered a metal-on-metal, very low pitched "chug-chug" sound every 11 o'clock pedal rotation when it's in the big ring. I tried to move the gears around and duplicate it in the smaller front ring, but no matter how much I tried to duplicate it in the small ring I was unsuccessful. It is a regular occurrence in the big ring.
I cannot see any chain rub in the front derailleur when it's in the 11 o'clock trouble spot, and I don't know where else to look for metal on metal. This is presumably a BB issue? When the bike is stationary, I cannot wiggle and jiggle the problem in the BB, it still seems perfectly tight to me. I don't know much about mechanics, so any words of wisdom are appreciated!
(I asked the guy very specifically if there were any headset or BB issues, he said no. I'm pretty confident he was telling the truth, because the way he spoke, he seemed to not have much knowledge about bikes, and bought it because he knew the parts were high end.)