High end companies do sophisticated things to make cables sound good. Lessor companies sound like the metal they use.
A big yes on that.
I use silver cables and found that a better made set exhibits none of the usual attributes bandied about on audio forums.
That, and cable synergy can go a long way, but I, myself, don't use all the same make of cable but when it comes to bi wiring, heck yes. Just to be clear, I use Cabledyne silver speaker cables and Darwin silver ICs and TWL copper PCs.
I've gone through the trouble of trying this and that cable to complement the ones I use on the lows and nothing really worked. I have a set from the same make finally figured out how to use two bananas on a single input, bringing serendipity to my doorstep.
As for mains noise, I doubt you'd hear it the way you describe. Mains noise, for me, was an overall masking of detail, air and focus that I got rid of by getting a power conditioner. I didn't think I'd hear that much of an improvement, but I did, and the noise you're hearing, I wasn't.
That, and you say the noise was already there and is now more apparent, so it could be the cables or they're clearing things up enough to hear that problem from somewhere else.
All the best,Nonoise