When I play the Polysix, every 3rd or 4th key I strike you can hear a sort of metallic, tiny metal clang sound over the normal patch tone. It comes out of the headphone jack as well. It seems to happen when the release knob is a little over the halfway point. It wouldn't bother me if it was at a very low volume, but it seems to be equal to the patch sound and is especially noticable at low cutoff settings. Anyone know what could be causing this?