I've notice numerous times in various bar/club type places that the acceptable vocal level when the band is playing, feedsback when the stop. i just ride the fader, or hopefully find an optimal balnce, and gate setting. or turn the monitors down a bit My guess is that all the stage noise is creating some kind of nulling effect and causing cancellation. and then when they stop i'm just amplifying the air and magnetic field. But i don't really have a solid explanation, if any does, it'd be great. or there could easily be an error in my technique. thanks!