Make sure your laser marker is correctly grounded and free from any static charge disturbance.

• Check if the Galvo head is making a constant buzzing sound. If so, then the problem could be caused by the main board. Replace it with a new, identical one.
• If the Galvo head is making an intermittent, buzzing sound, which happens even with the laser marker correclty grounded,

1. Measure the output voltage of the Galvo lens head's power supply. The normal reading is 15V.
2. If the voltage measures stable and right, replace the Galvo lens head with a new, identical one. 
3. If the voltage reading fluctuates, then replace the power supply of the Galvl lens head.