BC21 preamp problem

just purchased used preamp and last nite i hooked it up;
a hum was coming from the speakers that could be heard 8-10 feet away when no music was being played. i thought it might
be a problem with the ground, do tonite i used a cheater
plug; the hum was still there and now a loud pop comes from the speakers each time i turn it on/off. in addition, my amp goes in and out of a "sleep" mode with the preamp on

i'm afraid to turn this preamp on as it might blow the speakers. this is my first experience with tubes and felt the BC 21 would be a good starting point.

i hooked up my old SS preamp and no problems.

any help would be appreciated.

my amp is McCormack DNA.5(A revision), speakers proac 1.5
cables MIT/Magnan

thanks