Source 4WRD II flicker with Sensor rack

My church has 26 Source 4RWD II fixtures being powered by a sensor rack loaded with D20 modules.  The fixtures along my FOH 2 pipe will flicker at low levels.  The fixtures are set to DMX for dimming and we set all the D20 modules to full using a group on the Chamsys QuickQ 30 console.  The DMX is terminated and it is not even every light or everytime.  I would be open to any suggestions.