Hello there,
By this, I presume you either have a problem with in-game audio or the CB Radio.
I will try to answer both for you In-Game Audio:
There are a few things that could be blocking out the volume for you, one of the obvious ones is make sure you have your PC volume turned on/up.
You can also try going into the In-Game settings, clicking "Audio" and making sure all of your volumes are turned up.
If the above isn't working for you, maybe try a simple PC restart, it may clear the bug of no volume. CB Radio:
Please make sure you have the CB radio turned on for a start, the default radio is channel 19 which is where 90% of people speak.
Other than that, please make sure all of your audio settings are turned on/up.
Hope this helps you!
If not, I apologise, I hope someone else can help Many thanks,
Callum.