Refers to where you jokingly imitate the "momentary static" sounds of a 40-channel two-way radio when saying something, often accompanied by making a "thumbing the mike" motion with your hand.
If you wanna truly amuse others with your "CB-squelch speech" antics, you need to imitate the "transmit and receive switching" sounds correctly --- when you begin a sentence, first vocalize about a second of raspy-exhaled "radio hash" sound, then speak in an emotionless monotone as you "say your piece", and finally wrap up with a brief loud-static "sound byte".
Example: Raise your hand up near your mouth and make a "thumbing the mike" motion, then say, "Khaahhh --- that's an affirmative, Good Buddy." Then pretend to release the mike-button, while simultaneously making a sharp crisp "hkhauhhk!" throat-sound to imitate the radio's internal "send/receive" relay switching back and the squelch "kicking in" to silence the static