mijostyn Your's was an informative ah-ha post for me.
Hacks that we are, despite the systems star grounding we assumed a grounding issue but were very hesitant to lift the amplifier ground.
The three of us could hear a noticeable issue when those high level cables were connected to the JC-1 amplifiers that were powering the system. It wasn't a huge issue but once we identified it became one of those things you couldn't help but hear.