2018 JP6 buzzing like crazy

I just got a 2018 JP6 in a trade and love it but when I plugged it in, it was buzzing like crazy, diminishing a little when I touched the pots but not totally silent.

I took off the control cavity plate and found a black grounding wire from the jack placed to connect to one of the cavity plate screws but not to the grounding screw. The wiring diagram shows this black wire connected to the grounding screw and a flyaway wire going to the cavity screw. Am I correct?

Everything else looks OK…

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