I guess the assumption is that we talking about "amplifier noise," right? If you are talking about noise from your power, it makes sense that a power conditioner could reduce that noise doesn't it?
Also, I don't see why it is so difficult to grasp the concept that sometimes there is noise that you are not consciously aware of, but that you notice the elimination of noise when it is reduced or eliminated. For example, there was one occasion when I was listening to my IEM's in my car, and it sounded just fine, but then when took my phones out of my ear for a second to talk to someone and noticed the radio was on. I turned it off, put my IEM's back in, and the difference in sound was remarkable. The radio sound was not something I was actively hearing before I removed my phones, however. I have had similar experiences while listening to headphones while my wife is watching TV. I don't hear the TV at all, even if I listen for it and try to hear what is happening on a program that looks interesting, but several times when I have been sitting here withy my eyes closed, I have noticed immediately when she turned off the TV, or brought up an on-screen guide, which muted the sound. Thus, the notion that, if you can't hear noise or a noise floor, a reduction in noise or the noise floor will not be audible is not correct in my view. Just like you can't tell if you are looking at white or something that is absolutely clear until you see something that actually is 100% white or 100% clear in comparison. You might not think you are seeing fog or hearing noise until it is removed, right? Am I missing something?