I recently bought a shure sm57 to record my electric guitar amp. Problem is, while I am recording AND playing (so there's sound coming from the amp) there's a bzzzz when I playback what I recorded. When I stop playing (still recording) there's no buzz. Also, when I record my own voice, there's no buzz at all. My setup is like this: Electric Guitar (Fender strat) > Amp (Vox vt100) > Mic (Shure sm57) > Mixing panel (Behringer xenyx 502) > PC What could be causing this noise?