Update on the above situation: FIXED! It was the chain that was causing the noise. Put on a new chain this morning, then went for a 30 mile ride. Not even a hint of the noise. It is really nice to have my smooth drivetrain back!!
Now there are more questions that will take a bit of explaining. I'll try to be short.
This was mentioned in my first post, but I'll include it here: "Never remove or modify in any way whatsoever this external link, which is permanently identified by the stamped production batch number, since it has the calibrated holes needed to close the chain."
This batch number could be easily seen on the new chain. And there was no number on the old chain. So I'm guessing the LBS who installed the chain paid no attention to this. I haven't talked with him about it yet. He has used Campy for years, and one would assume he knows what he's doing ... hopefully.
If that link is indeed critical, then perhaps the noise developed over time because the chain was not joined using that link. This is possible, but I'm not sure what difference, if any, exists between regular links and the one with the number. Since one may break the chain again at a "regular" link and rejoin it, I'm not sure I understand why Campy insists on using this special link.
Second thing ... the LBS installed the chain pin the wrong way. It's supposed to be installed from the inside of the chain to the outside. And, he used a homemade or modified peening tool. I don't think a homemade peening tool would matter, as long as it was made to the correct diameter. And the direction of the chain pin -- would that really matter so much? I might call Campy next week to see what they say about these things.
The noise had gotten noticeably worse in the past week. The most noise was whenever there was side bearing on the chain from having the chain on either the largest cogs or the smaller cogs. When it was the straightest (from chainring to cassette), it was the least noticeable. Possibly noise coming from the peened chain pin with a small amount of free play in the bushing? Maybe play/noise is amplified with side bearing? With the unusual variables listed above, though, it may be hard to fully know. And there is the point of diminishing returns since the new chain works.