Brach and I see a number of possible sources of noise.
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The resonator. As we discussed, the higher the density & mass of the resonator, the more likely it will create a mysterious white noise. In my experiments. the best resonators also picked up ambient noise like crazy, so I couldn’t even isolate this source until I moved into a decent studio space.
The fine leads from the piezo are unshielded.
How are those fine leads attached to the squirly cable? Neatly soldered, I hope, not twisted.
You commented elsewhere that the shielding on your cable may not be great. It’s important.< The grouinding inside the box, which box, by the way, is terribly cool. You have the input jack, output jack and the board all grounded to the copper foil shield. Brach suggests you ground the 1/4" jack to the board, ground the board to XLR pin 1, then ground XLR pin 1 to the copper shield. This gives any errant electron exactly one path to ground, with the shortest, most direct path at the input source. Your current arrangement allows for a few ground loops, which likely accounts for the difference in noise between the two cases.
Try fiddling with some of those, especially the ground loops, and let us know if there is improvement.
I am going to move this conversation over to “Product Mods”.