If a Radio or TV needs to be audible. How is that written in a Script? Is it written like the characters, or is written in the description in parentheses?
I'd write it in the script. You have to hire someone to read the lines, and it's audible dialogue which the characters and audience have to hear and react to.
Number 13 on this page explains that
However, if its just background noise:
So, it appears if it's significant, it should be written like any other dialogue in the script.
The script for Night of the Living Dead - available here as a pdf - treats audible dialog from a television like dialog from the other characters (see pp. 5-6)