I know this post is a few months old, but wanted to say that I recently acquired a Halo A51 and have the same issue as the original poster. Prior to this I had a Rotel RMB-1075 which was silent.
The hum I have is audible from the unit itself once powered on and the sound is transmitted to all five speakers even when the receiver is completely disconnected from the amplifier. I have called Parasound for their advice, but seems like they may not have much else to offer.
The hum I have is audible from the unit itself once powered on and the sound is transmitted to all five speakers even when the receiver is completely disconnected from the amplifier. I have called Parasound for their advice, but seems like they may not have much else to offer.