Thanks to a cooperative service tech (and my Nikon D60), I see what's going on for my
problem. There may be some buzz from the transformers, but the majority of the buzz was from the heat sinks
attached to the high power transistors. Every one of those heat sinks on both the Y-board and Z-board buzzed. Digital Video Essentials DVD set to 100% white pattern.
The heat sinks are aluminum, which is not magnetic. The heat sinks are transferring board vibrations into something easily heard. I'm sure there's a nice complicated explanation, but it doesn't matter. That's what I hear. You really can't tell what's going on unless you remove the back cover. I didn't put my ear next to the heat sinks until I saw the tech push on them and not get shocked.
The tech replaced both the Y-board and Z-board. The replacement Y-board buzzed about the same level as the original. The picture was extremely noise and smeared. Apparently, you need to re-align the Y-board when it's replaced. He put the original Y-board back. Picture OK.
We kept the replacement Z-board because the buzz was a bit less.
After we were done, there was very little improvement. No amount of pushing on any board could change the buzz. The tech said to talk to Samsung because there was nothing further he could do. He also thought that this was normal plasma buzz. I didn't.
As a last resort, he took the black foam that was shipped with the Y-board and stuffed it between the back cover and both the Z-board and Y-boards. There was improvement! Turns out that the back cover is helping to amplify the sounds. With the foam, it can't vibrate, which brought the buzz to just within a manageable level. Barely.
Not only that, the TV speakers didn't sound like crap anymore. Now, they sound like simple cheap speakers instead of tin cans. The audio was resonating with the back cover (or something else inside), which would explain why I wasn't able to equalize the response.
The display was able to be serviced on its stand. Remove all the screws holding the cover in place. Remove the back cover. Put in at least 2 of the screws for the stand, to keep the display in place. Here's the view from the rear. I added text to show where the Y-Board and Z-Boards are located.
This is a close-up of the Y-Board. The Z-board uses the same design, so the picture is similar. I added the text. Those transistors are switching a lot of current. Note that the capacitors (red squares on right) are epoxied together. This was done everywhere on all the boards.
This is the black packing foam used to ship the Y-board. The tech placed it between the Y-board and back cover. Same for X-board and back cover. There is enough pressure with the cover on to hold the foam in place. The foam doesn't block the buzz.
Upon further review, there's a slight magenta haze on the bottom of the display that showed up in the test patterns. I'll deal with that in the owner's thread - not related to buzz.
With the back cover no longer contributing to the sound, the buzz is under control. If needed, I can do some external audio treatment around the display. At this point, it may not be worth the hassle to take a gamble with a replacement. It still has a really nice picture.