Help, HUM from California Audio Labs Icon MK2

I replace my Proceed CDP that gave a wrong digital signal to ADC with Cal Audio Labs Icon MK2 (HDCD). It sounds rather dark but okay. Imaging is great. But I am bothered by the hum it makes. I have never had such hum sound with Proceed. What's wrong with this Icon MKII? Is this from the background noise, or low frequency audible from the power line? I really wonder if I can reduce this hum substantially. Please give me some inspiration. Thanks.