Mark Levinson 383 problem - hum

I was on my way to bed last night and as I walked by my speakers (Egglestonworks Rosa's) I heard a noise. At first I thought maybe it was a ghost, but upon closer inspection it turned out to be an audible humm coming from my right speaker. I also discovered a humm coming from left speaker, though significantly lower in volume. Never heard this before - the speakers are new, but the amp is several months old

My system: Levinson 383 integrated, Egglestonworks Rosa speakers, Electrocompaniet EMC1-UP digital, Analysis-Plus silver cables all around.

The system was fully powered up, but the CD player was in stop mode. Putting the CD player in Standby did not correct the problem. At first I thought maybe the speaker cable was picking up noise from some TV / DVD power cords that ran by it, but unplugging that system at the wall did not correct the problem. All connections were tight, audio system cables were all properly isolated (i.e. no tangled mess of speaker cables, IC's and power cords). The only thing that solved the problem was putting the amp in standby mode.

So I have many questions. What is causing it - how do I fix it? I prefer to leave my system fully powered up - not in standby - is this bad for the system? Is pumping a contious hum/hiss through my speakers detrimental to their long-term health.

I am calling my audio dealer today to get them to look into this, but I live in China (Shanghai) and language is sometimes a barrier when the conversations get complex (as this one will undoubtedly become)