Sometimes I have the same while flying. But not always. I know military radios can have a frequency coded system so that other people cannot listen to what is said, but that cannot be the case here since it is a civil known frequency.
(the system works by varying the frequency in a very fast way eg 120 mhz, 120,5 mhz, 119,5 mhz,...; the code of change in frquency is only known by the rx/tx).