Discussion about the Korg PolySix synthesizer

OK, a breakthrough of sorts...I thing this is a ground loop or something. When I touch the metal bracket for the keyboard onto the grounding plate that covers about 75% of the bass of the synth, the noise significantly returns. When I left it off the noise subsides to a significant extent. Still doesn't go away but nowhere near as loud. Any thoughts based on this discovery? The silver floor surface appears to be showing continuity with ground and seems to be getting this ground from the MIDI ports rivited to the body.