I got an Ampeg BA-115 for Christmas to use in the coffee house style youth service my church has in our youth room and last night was my first chance to use it in that setting. I've played it a few times at home and besides a loud humming I didn't notice anything out of the ordinary. Last night, however, I noticed that when I had the volume turned up much at all and attacked a note somewhat harder than the rest I would get a loud obnoxious crackle sound. I could unplug the bass from the amp and the humming and crackling would continue. Once, I even had the power off and someone said something into the microphone and my amp crackled. What is causing this?