If you believe your system otherwise checks out and there are no identifiable connection problems, grounding issues or faulty components and all that, then you are very likely indeed looking at electronic noise. This can be thought of as noise from the power lines coming into your house, but is actually EMI/RFI in general which also comes into your system through in-wall wiring, from within your components themselves and even through the air. There's also the issue of power supply crosstalk that's too lengthy for me to go into here, but it looks like some form of power conditioning solution should be on your system to-do list. Your assumption that that the noise may be preventing you from hearing all the music is correct, but likely much more than you may feel you have reason to suppose. There is the noise you can hear itself, which as you rightly point out can have a masking effect. But, there's also the purely electronic component to the noise which is far more destructive to the sound than most 'philes realize because it obscures the sound signal before it ever reaches the speakers...and that sound you never hear no matter how loud you turn it up or how good the system is. This second, purely electronic, effect of noise typically has a far greater adverse impact on the sound than the above acoustic one, but when the acoustic problem is present enough to be problematic you can bet the acompanying electronic component of the noise is disproportionately large and would well benefit from some power conditioning. PC has been around for a good couple decades or more so there is a ton of it out there these days, but traditionally there have been problems with getting it to properly filter out the noise without also restricting the audio bandwidth as well. Any more, all-in-one-box-solution power conditioners in the big leagues START at around 5 grand, but none of that is what you'd need to be looking at...IMO no one does, really. The one-box designs necessarily can't take into account the EM/RF problems with in-wall wiring and through the air, anyway...let alone they're unnecessarily expensive. For my money, I'd try going to Alan Maher Designs' facebook page and at least see how inexpensively things can be tried and/or get done. His new Quantum solution is what I'm talking about. Yes, I've tried it and no, I don't work for him nor am I acting on his behalf as anything other than a satisfied customer. Consider other options as you will, it's just that I don't see how you'd be able to impact the problem more effectively for less money (we're talking 40 bucks here, for something called the Q-mini, to dip your toe in the water, and even that may do it for you). You need to become a facebook friend of Alan's before you order, but he'll help you with that and all the rest. But, the main thing is that you'll not just be pleasantly surprised by the effects of good power conditioning, but absolutely blown the f away by the difference it makes...I mean, if not, then I think you may be doin' something wrong if you know what I mean, but I think you easily stand to come away from the original problem with the sound of a whole new system. Hope this helps.
