When I was a kid I’d disassemble everything I could get my hands on from phones, laptops, game consoles etc. I was obsessed with finding ways to modify them to make them run better and part of that obsession also meant repairing things that broke or went wrong.
The saying you “can’t teach old dogs new tricks” has some truth to it when you consider the extraordinary stubbornness of so many individuals. Such is the nature of some people who grew up when through hole technology was the only type to exist and then surface mount came along...
With the many manufactures of capacitors these days you are bound to run across some part series designated for “Audio use” with little other info available to explain for what audio purpose specifically they are intended for and what makes them so great.
Anytime you have an amplifier that is generating unwanted noise to the speakers you first need to determine what type of noise it is making. From there you can determine the likely source of the noise and rectify it.
Common mode rejection ratio is the ability for a device to reject or suppress “common mode noise” -that is noise that is common(identical) to both differential input channels. Let’s take an amp for example with an audio signal at its differential(inverting and non inverting) inputs.
In most amplifier designs you will be tasked with choosing an input filtering(coupling) capacitor value. This is the capacitor that goes on the input stage of an amp and filters DC bias from the audio signal.