You would set the 2 speeds and use interval with idle mode. One pump should be in socket 1 or 2 and the other in 3 or 4. In this way the pump can be at one of 3 speeds at more or less random, 30% being idle, and the other 2 you set. You would want to set a short interval of about 1 minute and a short pulse of about 3 seconds. This would be the closest to a random. Ramp mode would add further variation as the pump would accelerate between these speeds.