Good Morning,
Please check the below in order to try to solve this issue:
- if you have a jack audio cable connected to the front of the amplifier, please remove it and check if the issue persists
- disconnect the board from the computer and connect an external device such as a MP3 player to the front of the amplifier and check if the issue persists
- if you are using a laptop, disconnet the power supply unit from it and check if the issue persists
Hopefully, these steps will help you to determine what is the source of this issue.
Thank you,
Miguel Silva
Promethean Technical Support