Simply as I could. The referred noise is from the power supply, usually not so good switching ones are used in Pi/PC. It can be pretty demonising regarding SINAD but that's about it. It's not what cause clicks and pops other sources of inter modular distortion in severe form can like for instance high straight radio waves. Each chip (DAC, AMP) has declared rejection rate of inter modular noise (but not up to the bottom of the spectrum at the advertised level), some are more prone in picking it up than others. This is more present in portable designs on properly designed desktop gear it's attended in many ways (larger capacitors, separate and better power lines, better separation between components and isolation...). The fix; better cleaner source of power either that you use good old deacent mobile phone charger or insert some power bank that you have lying around in between. Again this won't be hear able as some obvious deviation but it will be measurable regarding SINAD.