I have a Mackie DL1608 with preset shows set up for the different configurations of the band. Sometimes we mic drum (kick, snare and overhead). I have the drum mic set up in all preset shows whether we use then or not. Last few show we have not mic'd drums but I am getting a level signal in the drum overhead channel. Input has nothing plugged in to it and input gain is all the way down. The signal pulses with the music, so it is not just random noise. Any ideas what this could be?