apples and oranges.
More than one culprit when it comes to induced noise and the means to rectify it
AC line induced-plenty of products out there , mostly the info is here.
But for me at least there are times when a line filter SCREWS UP the sound.
Sorta beats down the dynamics and present an overall uninvolving boring sound so I only filter the line at video and digital sources.The amps and line level stuff is "out there" naked.
RF signal induced.More of a problem in a high gain situation such as with phono or mic preamps than with the average componant.But still it never hurts to have some RF caps at the inputs and shielded cables (something I rarely use and never have a problem but I have all short runs)
ultrasonic digital artifacts-lotta stray crap floating around in computers , VCRs ,televisions, etc.
Look at the back panels and youwill see FCC compliance codes !
Damn transmitters !
And do not for a moment think the FCC gives a rats ass about audio quality in the home , they do not.
They are only worried about a signal radiating strong enough as to interfere with other devices in the home or even outside the home ,such as the neighbors TV picking up your microwave.
Audio equipment on the whole is pretty well designed in these times but the final frontiere for good sound is putting your system in a "bubble" .
That is isolated itfrom ALL things not related directkly to the sound of the actual componant.
And that includes electrical as well as mechanical interference.
Isn't this fun ?