@chocaholic
Re: mains connection
Poorly designed components (or components that didn’t look at this issue) can have leads that act as TRANSMITTING antennas of noise.
Given the rats nests of interconnects and power leads in the back, I wouldn’t be surprised, at all, if an interconnection doesn’t pick up garbage transmitted back out from an unshielded power cable, especially if they are touching and follow parallel for a fair length.
My theory is based on a sample of one, where the power cord of my turntable laid flat against my phono cable and I could (and anyone could) hear a hiss until the two were pulled apart. Kept happening due to how everything was smashed together in my original set up.
Went away when I switched to an Amazon (nothing fancy, but definitely shielded, you can’t detect current with a “live wire” detector) mains cable.
Mind you, the phono cable is the thinnest interconnect and the MC signal the weakest signal in the chain. So the most vulnerable.
When I redesigned my rig, it made me run all interconnects XLR (including phono), picked fully balanced components (including phono amp) and took great care lay out wiring with a considerable air gap and no touching.
it’s also super sharp looking behind the scenes which makes my OCD very pleased. LOL.
Not fancy wiring, either. Mogami platinum with high end furutech ends. Speaker wire is larger gauge pure silver from a military aircraft (used for fire reasons), braided by my daughter. I doubt all in its $1000.