When you are speaking on stage, be sure to turn your cell phone completely off.
Many cell phones and other wireless devices cause interference and noise with microphone signals. (Blackberry devices cause serious interference for all manufacturers’ microphones.) Even if the ringer is shut off, a cell phone periodically transmits any time it is turned on.
The frequency, or radio wave of the cell phone transmission, can get into any audio gear located within a few inches. The worst scenario is a phone in a pocket next to the lavalier mic. To be on the safe side, keep all cell phones a foot or two away from the console and the mic.