EchoSpot's post in Help! How can I mute the voice volume on ETS 2 mp as all I can hear is people shouting down their microphones! was marked as the answer
You can turn off the CB radio.
1. Press "TAB" to display the player list
2. Look above your seat and you will see the CB panel
3. Right click to activate the In-Game mouse pointer
4. Click the button furthest to the left on the CB panel