First of all, the mighty scan fixture is a older model and requires a duty cycle. In short the light requires a break from use every 15 min. They are not meant to run for hours at a time.This also means that you don't have to unplug it every 15 minutes but keep it in blackout mode for at least 5 min or more between every 15 minutes of use. The buzzing sound that you are hearing most likely is the solenoid that controls the lamps on and off function. When you are running the unit on a dmx controller and you press the blackout button, you hear a click sound before the lamp turns on or off. That click is the solenoid either being energized or not. If the lamp is flashing on and off, do you hear a clicking sound? If you don't. The thermal breaker near the lamp may be causing the flashing.
When you first plug the unit in, it should go into reset mode then the lamp should stay off unless you have the dip switches set for stand alone or your dmx controller is not in blackout mode. The lamp should never come on during the reset process. The reset process should only run when either plugged in, temporary loss of power, or dmx channel 5 is at the full on position. If you have dmx channel 5 fully on, the unit will constantly reset it self.
This information is to let you know what the unit should or should not be doing in order to help you diagnose the problem as there are so many factors that can cause a failure. It is impossible for me to provide a solution sight unseen.
Hope this is of some help,
DJT