I don't have a definite answer for you, but I have heard the same phenomenon on occasion, and usually in the higher channels (30-40). I don't hear it all the time when there's skip, as you do, however. What I've heard mainly is what sounds like pulse bursts, changing in phase or duty cycle, somewhat similar to the demodulated audio I once heard from a Radio Shack "high-end" RC truck (one of their $100.00+ jobs). It was a 27mhz signal, with some kind of pulse width or pulse phase modulation on a couple different audio frequencies. Whether you're hearing something similr, I don't know.