Wrapping power cords and interconnects with copper foil.

@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.

@richardbrand Agree that right angled cables minimize transfer of electromagnetic signal... Parallel cables promote transfer, much as transformer or RF coils are wound in parallel with each other. 

But... for the whole group.... do want to remark the following: Copper or aluminum shielding is NOT a “snake oil” fix— as some have posted— but rather is based on established principles of physics. Shielding of audio cables from electromagnetic applies function of a "Faraday Cage," which creates a barrier between the internal components of a device and the external electric fields.

@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.

@joelepo @richardbrand 
Unfortunately this is not a group about engineering or physics most people here seem to be interested in the hobby more than the engineering principles. Sad people who love listening to music so much have such low regard for the foundation of their hobby. 

@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!