Is your power cord or SCSI cord touching or running along the 1/4" cords from the out/in from the MPC. Maybe your SCSI cable is touching the speaker wire.
Try isolating cords ... just do everything - you'd be surprised the wierd shiitt that happens in different situations
peace
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With knowledge ...
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Comes sorrow.
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.No Jesus? No peace. Know Jesus? Know peace.
Word of Warning with regards to cables.
Have your Audio Leads run in one Direction. and your Power Leads in the other. So that your audio leads dont pick up frequencies and static and all type of sheg that will mess up your music.