It's NOT feedback. Feedback is when the sound coming out of the speaker is reproduced again because it's being picked up by the pickups (or microphone). That buzz you get is because you're touching the hot of the plug, and the currents in your body are sending some electrons down the cable. It'll change depending on whether you're also touching the ground connection.
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"Without space, music is just noise piling up on itself." TRK
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