What I think you are hearing is noise being digitized. I have the same sort of sound on my fire/aid feed
. I do not mean the hum you here when there is no talking, wait for some action.
My Police feed does not have this noise, the only difference is my fire/aid feed is using the on-board soundcard and my police feed is using a soundblaster in the PCI slot in the same computer.
Only solution is a better soundcard.