once again as rockonn91 said its prolly reverb. my guitar teacher bumped the marshall half stack at the guitar school and it made a huge buzzin noise and i was like whoah wats that, and he was like, thats just the reverb. so i figure it'd be the reverb :P i have had dodgy cables that have screwed me in the past but thats more to do with the connectors, say if you twist a connector on either the amp or the instrument side a cheap connector will make a bit of a buzz.