A lot of high freq noise is airborne - it has nothing to do with whats plugged into the mains - this has the effect everywhere there is mobile phone masts, wireless etc. Which is everywhere and all the time.
Then you have other things on your own mains as well in close proximity - especially if your system is shared av - has a tv sky box router etc all with smps supplies, or streamers which are basically pc's.
So to me everyones system is affected all the time - if you tried a product 10 years ago - the effect could be very different to today. Thats why demo's like what I posted to are great because you can go along and hear without any hassle messing with your own system, no cost involced - but you get to hear what the benefits might be, then decide if you want to try at home. I bet 99% of home demos of good mains products result in a purchase.
The good units are bloody expensive - but they do a grand job. I am in a big way surprised CNo heard negative benefit from a Super Titan - thats bewildering to me. However I ask are people so accustomed to hearing noise on the systems that sound is what they associate with correct sound - just like when vibration is added to the sound. When its taken away its like something is missing from the sound - well that is true, whats takne away wasnt supposed to be there.
Even a seasoned listener of many years can be so used to hearing it sound the wrong way - its actually ingrained on them as right and it takes some time to realise and accept the new sound as correct. Once you have heard it and accepted you can never un hear it and the previous way will always sound wrong, even though it sounded right to you for so long.
Everyone must have experienced this with either a piece of kit change, speakers change, layout change etc.