Wrapping power cords and interconnects with copper foil.

Just like to point out that, weight for weight, aluminium is a better conductor than copper.  Copper usually weathers to a green colour - verdigris.

Consider whether the RFI carried by power cords is actually generated by the components they power, not by the wall supply!  Much more plausible ...

@tubelvr1 

Just interested, did you wrap all of your cables at once, or was it done progressively?

It is not clear from your description whether your wrapping was floating, or was grounded at one or both ends of the cable?  You did not mention speaker cables?

I would expect the greatest difference to result from wrapping the phono cable, where the signals are miniscule compared with line-level interconnects.  I presume your phono cabling is RCA, not balanced? 

Surely wrapping the cable changes its capacitance, which may be good or bad considered from a system neutrality perspective.

Another cheap treatment for power cords is to snap on ferrite rings at a cost of a few bucks each.  These can really clean up digital noise coming from components, especially if they contain switch mode power supplies (computers, class D amplifiers, etc).

@joelepo Yes, good practice is to keep power cables away from audio and data cables, as far as practical.  If they have to coexist, try to cross them at right angles or thereabouts.

@joelepo Agree on the physics of the Faraday cage, which is based on the repulsion between electrons forcing them to the outside of the cage, thereby isolating the inside from external electrical interference.  Mind you, nobody knows what an electron really is.  Richard Feynman, who came closer than most, notes that every electron interacts with every other electron in the universe.

Magnetism is something else again!

Consider this for power cables: the RFI may be injected by your component and is not necessarily from the mains supply or from the 'ether'.  I have a KEF subwoofer with a class D amplifier built in which totally destroyed my weak digital TV signals until I popped a couple of cheap ferrite chokes over the power cable, which had been acting as an antenna radiating RFI into the 'ether'.

We now know, thanks to the greatest failed physics experiment, that the 'ether' does not exist and as a consequence space-time is relative ... another story.

@donavabdear Neville Shute (Norway) said that an engineer was somebody who could do for 10 bob what others could do for a quid.  In other words, provide very cost-effective solutions. 

Understanding some basic physics would save some hobbyists thousands, if not tens of thousands, in my opinion. 

I am not sure if you meant "Sad people" or "Sad, people ..." or even what you meant by "the foundation of their hobby".  Taking out the double negatives from "Unfortunately this is not a group about engineering" gives "Fortunately this is a group about engineering" but I suspect you meant the opposite!