zenguitar wrote:OK, this is a long shot, but the symptoms are reminiscent of a problem that would sometimes appear in early shallow drilled Strat trem blocks.
In the Strat, the length of string inside the trem block could vibrate in sympathy and on occasion would buzz against the sides of the hole. That's why Leo revised the design to drill the trem block so that the ball ends were deeper inside.
Looking at your photos, I see that the tailpiece has a deep section between the front edge and the string retainer. And that leaves a row of 6 deep drilled holes. Looking at the photo taken from the endpin you can see that the ball ends are all in a straight line. It's harder to tell from the other photos, but it appears that the strings exit the tailpiece in a straight line as well. However, the top of the bridge and saddle isn't flat, it has a radius. That means that each string is coming out of the tailpiece at a slightly different angle, and that might be enough to bring one or more of the strings close enough to buzz against the sides of the holes through the tailpiece.
The best way to check is to get 3 wooden cocktail sticks or toothpicks. Cut them in half so you have 6 short sticks with pointed ends. Then push one in each of the exit holes from the tailpiece so you wedge the string against the hole.
If that does fix the buzz, the fix is to remove the tailpiece and re-drill the holes with a slightly larger drill bit.
As I say, it's a long shot. But it is a known cause of hard to trace buzzing.
I tried this. Toothpicks jammed in there. No effect.