I bought a used Genzler mg800 from GC, and I have a schroeder PS212 cab (untested before this). I think what I'm hearing is the fan being amplified through the speakers. The volume is completely turned down on the Genzler. I've tried moving the head and a different outlet. Unfortunately, I don't have another head to test with, I'll probably have to bring it back to Guitar Center. Do you have any thoughts on what this could be?