Well a blank reading is usually a broken connection somewhere... or a short that shouldn't be.
It's easiest to check the (four?) LEDs by just turning the lights off.
The noise floor varies. I've had one that was silent and two that had a low noise floor. It could be the tubes, the twisting of the wires, or how the voodoo plays out. Do you have different tubes to try? I might have a spare input tube to try, but don't have a power one.