I'm playing in my school's talent show variety music thing, and our actual evening shows are coming up. My rehearsals went fine, but just this afternoon when we did a matinee for a bunch of Jr. Highschoolers, about halfway through the song I got this continuous hum of freedback. It made the song sound pretty terrible, but it never happened before. I moved as far away from the amp as possible, but it still continued. I muted the strings after every piece of riff, but it still came back, and even when I turned my volume down almost to zero, it still came back. I have no idea what could be causing it. I know I'm standing far enough away from the amps on my side of the stage, but is there anything else that could be causing it? After the show the techies told me that "you are causing alot of feedback. You should probably do something about that." But I have no idea what I'm doing wrong. There's mic stands right behind me and and an elevated drum kit behind that. What I don't understand is, there was no problems during rehearsals. Even when I stood right beside the amp. The performers are not allowd to adjust the amp levels at all, and the techies control all my volume. I don't know what to do. If any of you can offer some advice, I'd be very thankful. I have my first real evening show tomorrow and I don't want to screw it up for the singers.