I am in a new top40/classic rock trio. Guitar player is now using this receiver http://www.shure.com/wireless/pgx/pgx4.asp for his guitar and his vocal headset (http://www.shure.com/microphones/models/wh20.asp). 2 separate receivers/transmitters. I have the exact same set up for vocals. I use the Samson Airbass for wireless, as well as a Rolls in-ear monitor system. Both are fixed frequency. The Shure receivers are multi-channel. Anyway, we were playing last night and were getting these "Whoompf" spikes during songs - thats the best I can describe it. It was like a power surge or a sound surge that lasts for a second then is gone. I stood by the board and monitored it and one of these whoompf's happened. I notice that both vocal channels (he's in output 1, I'm in 2) clipped - all the LEDs shot to the roof then went back to normal. We changed out his mic cable and things kind of calmed down but the whoompf came back. Anyone have an idea of what it might be???? With all wireless channels uncrossed we should have been fine, no?