When an (internal) PC is connected to a touch screen it will give a notification sound if you switch between the Android and the Windows environment (For example when using the screen's annotation tool) Windows will play a notification sound by default as it recognizes an USB (touch) device. If you like to turn these sounds off? Please follow the next steps:
Touch the speaker icon until the following menu pops up. Now select sounds
Now scroll down in the [Program Events] box until you reach Device Connect and change the associated sound in the pull down menu to 'none'
Repeat this step for the Device Disconnect in the [Program Events] box and you're done.