That's why it took me so long to figure out that the racket after my first shift was being caused by the front derailleur. It was quiet in the gear I started in. I shifted and then kept moving it back and forth trying to find the silent spot for the new gear and it just wasn't working. I did look down at the front derailleur and it "looked" OK (my vision isn't sharp), so I kept fiddling with the rear. The fact that I was able to get back into the gear I started in and have it silent should have tipped me off. I guess this is a case of bias-induced stupidity -- I expected to have trouble finding the right spot for the rear derailleur, so I believed that had to be the problem.