Suddenly my JMP head is buzzing like crazy! And when I kick on my compressor it gets louder. I ran my pedal board through two other amps; not the problem.
What could it be? I had this head serviced/tubed, etc. around 6 mos. ago.

Could be a bad ground connection somewhere in the amp. Also, do you have a three-pronged plug? If not, you may have plugged the two-pronged in upside down. Or, if it has a ground switch, just try flipping the switch the other way.