Did you shunt pin 1 on the XLR terminal straight to the XLR case?... and the XLR jack has good contact with the case?
yes, i did. my DMM shows good continuity between the face panel and each XLR case.
Distance is also your friend. Position the transformers and AC part (fuse, IEC) as far away from the preamps as possible.
for sure...this metal enclosure is 8" deep, just like the plastic test box, and the first two channels of preamp are farther away from the trafo than in the test box. the last two channels (when i build them) will be about the same proximity as in the test box.
one difference between the metal case set and the plastic test box is that in the metal case i have the PSU board mounted vertically on the rear panel, as opposed to horizontally on the floor in the test box. i shoud try repositioning the PSU board to see if there's any noticeable difference in AC/RF noise.
finally, i have also decided to replace my manually-twisted signal wires with some Canare StarQuad...it's got two insulated twisted pairs inside a tightly braided shield - at this point i simply don't want to wonder if my wiring is as quiet as it can be.