I have some 60 cycle hum when I play in a certain building. I go to the local college in my town to participate in their jazz workshop, but whenever I go there I always get a 60 cycle hum coming through the amp. But whenever I plug in my bass somewhere else through a different amp, there are no problems. I double-checked the wiring, and everything is done correctly, I even took the time to shield the cavities. The two amps that we switch back and forth on both have the same problem. There is a Gallien-Krueger MicroBass 1x12 combo, and a Markbass little mark III through a 1x12 cabinet. I've tried pressing the ground lift button on the back of the Markbass, but it doesn't do anything. I'm running a standard jazz bass. I'm assuming that the outlet that we plug into might have the ground disconnected or something like that. Does anybody know what might cause this/know how to fix this? Any help would be great!