Fundamentally, broadcasting static during a call is a sign of the fact that signal power is degrading (or that there is no sound coming through whatsoever). When signal strength degrades sufficiently, the static resonance emerges.
When there is no communication coming through, it’s a slightly separate story. A walkie talkie has what’s renowned as a ‘squelch’ monitor circuit that keeps tabs on the signal strength. The squelch circuit will mute the amplifier when it realizes that there’s no signal coming through into the device. This is, fundamentally, the exact same purpose as your Television has as soon as it cuts off an unavailable channel after a fixed time. However, in the moments before your 2 way radio ‘squelches’ the signal, you’ll hear static, or ‘white noise’ as it is also called.
‘Squelching’ is a fairly vital part of any/all broadcasting gear. The method used in your 2 way radio known as a ‘carrier squelch’ is more likely to be manually adjustable.
From Wikipedia (as of may 2013):
So what’s ‘white noise?’ In accordance to Joe Shambro, writing for About.com’s handbook to home recording,
“White noise is a static sound that has equal energy on every frequency. Think about this for a second: every frequency from 20Hz to 20kHz is equally represented at the same velocity; this type of frequency scale is called a “linear” scale. This gives the noise a uniform, static sound that the human ear detects as somewhat harsh and heavy-handed toward the high frequencies. However, white noise represents a very unnatural way of presenting frequency data in terms of how our ears work.”
If you are experiencing sound degradation on your 2 way radio, there may be a number of causes for this. ‘Wireless Woman’ a writer with an excellent website about two way radios, has this to state:
So here you have it.