I'm in the middle of an assembly in our theater. Since I'm bored in the booth, I started turning the small desk fan that we have next to the sound board on and off. I started to notice whenever I turn it on or off, there is a small pop over the main speakers. I listened to the individual mic and the main using headphones and the pop is not coming from the board. There's also no talkback mic left on (unplugged it to make sure). We're using a LS9 if that makes any difference. This has happened once or twice before. Anyone know what's causing this and how to fix it?