Guitar processor noise...? BZZZZZZ!

The bass has no battery in it so Ill have to dig into the wiring to find if I lost a solder joint. It was a bass that a guy put together for me so who knows what the electronics look like. I see ground in all these schematics....where is the ground in the guitar.. The ring of the jack? I see a few schematics that show a wire going to "hardware ground" but nothing that look like an external connection. Is that just a reference to common ground through the cord?
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