Hey Jeff,
Sorry for the delay in response! This is an issue near and dear to my heart. I'm hoping that we can sort this out together because, to a certain degree, I suffer from some similar problems. If you want to skip to the meat of this post, please do. It's at the bottom.
Let me issue this disclaimer first: I am no electrician. There's a lot I don't understand about electricity in general. I've committed to learning and have started gathering resources to do so. Until then, I'm going to lean on the helpful advice from an electrician friend of mine. I hope to have some input from him soon. Until then, my little story:
Of the the very few electrical outlets in my home, not a single one is grounded. They've also lost their "grabbing power" so it's tough to keep things plugged in. As you can imagine, this situation brings with it many headaches. As a result, I've had to do what I'm certain would horrify electricians everywhere (I'm kind of hoping for a bunch of responses telling me that my house is bound to burn down any day now) I'm using "Cheater Plugs". If you aren't familiar with the term, it refers to the "3 prong to 2 prong ground lifting adapter" I think I'm using something like 6 of these in conjuction with good quality surge supressors.
For the most part, I've managed to go without noise in my main system upstairs. Fairly recently, I added a "Frankensystem" in the basement comprised of old prototype speakers and partially defunkt electronics. It's a home theater meets computer audio meets recording studio thang. Surprisingly, it sounds amazing.
Whilst making some changes to the wiring configuration, I noticed that I was being electrocuted. It sounds funny but that is more or less what was happening. I was in my socks, firmly grounded and grabbing on to rca cables and I noticed that my hand felt funny... it was a lot like sticking your tongue on a live 9 volt battery. I traced it back and determined that it was being passed through an old fisher receiver (a component with an ungrounded plug to begin with)
I don't know how this is happening, but it is clear that there are all sorts of electrical issues at play in this setup. I intend to use a Monster Power center to see if it makes any difference. I don't know that it will but it will be a fun experiment. So how does this tie into your situation?
I, too, was getting noise when using a Coax digital audio cable. It disappeared when I implemented an Optical cable. The reason why has to do with the fact that the 1s and 0s of digital code get passed electrically through a Coaxial type cable whereas they are passed by way of light pulses with an optical cable. You noticed the crackling and humming changed when lights were turned on and off. This is an indication that they are having a direct effect on your equipment. Essentially you have "Dirty Power"
Cleaning up dirty power is one of the big marketing points of these higher end surge supressors. To what degreen can it "clean it up"? I'm going to find out this weekend and let you know what I discover. I've always maintained that there is a price tier where true value can be achieved. If you spend $150.00 on a device that protects your system to the tune of $200,000.00 (insurance) and actually need it once in its lifetime, then it just paid for itself.
Caleb Denison