Last night, I was at one of my extremely rare band practices. I was there before anyone else, so I set up my stuff and planned to just fool around on guitar until they showed up, but my amp wouldn't work. It was switched on, but no sound would come out. I thought it might be a lack of power at first, but the power light was on. I thought it might be something wrong with the guitar, like a loose pickup wire or something, but then I realized I had just plugged it in to my tuner and it tuned fine. The only sound it would make was when I unplugged a cord, it would make a loud reverb-spring noise. Anyhow, I started slapping the sides of it and rocking it back and forth, and after a bit it just sort of.....popped....and started working fine again. Anybody have any idea what that was all about?

My amp's a Fender Frontman 25R.