Please consider the following:
Mute your device by pressing the 'MUTE' key on your remote. If this sound is gone it is probably an issue with your playout device. If you still hear this sound while the device is muted it might be an electrical/electronic issue or a problem with the screen itself.
To discover a potential playout device or wiring issue please select different source inputs (HDMI1, HDMI2...) to hear if the sound is related to only one of them. If this issue is related to a single source input and disappears once another source input is selected please disconnect this source playout device completely from the screen and check/replace your playout device or wiring.
To discover a potential electric issue please make sure your screens power adaptor is connected to the same electrical circuit (phase) with your playout device(s). The easiest way to assure that is by connecting all devices (screen, playout devices, receivers...) to the same electrical wall socket.
Last, disconnect everything from your screen except the speakers and the power adaptor. If still you can hear this sound please contact ad notam's support.