ARC 100.2 pop and hum

I just got a new ARC 100.2 solid state amp. When I first turn it on, there's a pop or thump in my speakers. Then, after the protection circuity goes off and the amp is "live," there's a hum in the speakers that can be heard as far as about 3 feet away from the speakers. The hum is evidently the sound of the amp. Getting close to the amp, I can hear the sound of the transformer(?), which is the same hum that's coming through the speakers. I've tested all of the possibilities of something else causing the hum: I removed the interconnect with the preamp--still the same hum; I used an adaptor or "cheater" plug to avoid the ground in the circuit; I plugged the amp into a separate circuit. Despite all of these different configurations, the same sound of the amp comes through. Is this normal? I'd expect it to be nearly dead silent when nothing's going through the amp, but maybe I'm wrong. Please let me know of your experiences with this amp and other amps. Thanks.