No new thread needed. It has been covered on ASR many times.
Use a common mains circuit to power the equipment, if necessary from one power outlet on that circuit.. Dwelling Earth may need to be up to spec.
Follow:
https://web.archive.org/web/20180720124823/http://www.rane.com/library.html#gpm1_1 Wiring, interconnection and grounding.
https://web.archive.org/web/20180720124823/http://www.rane.com/library.html#gpm1_1 Those on level controls.
https://web.archive.org/web/20180722055456/http://www.rane.com/note149.html
Good connectors and properly shielded cables are preferred(they don't cost much).
Inherently noisy gear probably can't be silenced.
Being able to understand and implement the above is required.
I had already made it clear that I may have been lucky with getting low hiss LSR 305Mk11s. But then others may not have set theirs up optimally. Who knows?
My old house has old but safe wiring. No UPS or mains conditioners. I have 16 mains items plugged in for my audio system. No hum and no hiss.
So stop the moaning and work it out, one way or another, now you know how.