I put this video together to help demonstrate my problem:
I forgot to mention in the video, but my entire rig runs through a Monster Pro Power 2500.
Does the sound go away when you mute your problem mic?
Here are some things I would try:
If it goes away when muted, it is likely RF interference so please move your receiver away from speakers and radios. You can also adjust the squelch level on your microphone to reduce RF levels when not in use.
If it doesn't go away when muted, please try another frequency on your microphone; if you are around the 800MHz range, try to go near the 550MHz range. HDTV and other sources can interfere with wireless microphone signals.
It sounds digital to me but it could be from your mics being too close or different sources accidentally sharing the same channel frequency. If all else fails try a different wireless mic.