So I just got a GK MB112-II about 3 weeks ago from sweetwater. It was a demo model and fot it for about $50 off new, but when it arrived there were absolutely no signs of wear. Ofcourse a few days ago I tossed the box and paperwork it came with... Got home today and plugged in to practice some and I get a pretty bad rattling noise on the lower end. Especially bad on open e for example... This was my first amp as I had only ever played with headphone amps. I was really happy with it up until now... Im pretty irritated and would like to fix the issue myself as I really dont want to pay for shipping the thing all over the place. Any suggestions? Thanks!