try a pair of headphones first to see if its the speakers. otherwise this tends to happen if you plug into the microphone Jack or the plug touches bare metal/grounding issues. I would disconnect the front panel connectors from the board and try the back to eliminate a.problem there (like a short/ground causing feedback).
you could also try a ferrite choke to eliminate interference
I cannot hear the noise from the headphones, but this is most probably due to the static being too quiet to hear without the boost from the speaker power source?