Amp buzz in speakers

I have an Aragon 4004 MkII amp, brand new Yamaha Aventage RX-A1040 receiver, with B&W 802 Series 2 speakers. I recently installed the system in a new rack system and am pretty sure there is very subtle yet audible hum/buzz coming from both speakers. It doesn't sound like a ground loop as the noise is coming from the mids and tweets as well as the woofers. I'm only mentioning these components as I believe I have narrowed it down.

With only the amp turned on(same with receiver turned on), the sound exists. Volume adjustments have no effect on it. Turning off the receiver has no effect. If I unplug the input cables to the amp, the sound goes away completely. If I unplug only 1 input cable, that channels sound goes away. I've tried different interconnects and all product the same buzz/humm. I've checked for nearby power cables, wall worts, etc, but nothing is close to them. I've also unplugged each of the other source components with no difference.

If anyone has any recommendations, I'm all ears!!

Thanks,

d