OK- this is a little related to AlexO's post about the Hydra 8, but mostly just about how weird electricity can be, and how difficult it is to ever completely isolate your audio system from the rest of your house. This a longish post but I think will be instructive if you stay with me. 
So here's my setup, which I wrote about before. I have a dedicated outlet that incorporates the PS Audio Soloist In-Wall Power Conditioner. My amp goes right into this outlet via an upgraded power cord (Harmonic Technology Pro AC-11). I don't think the Solist does a whole lot in the way of actually regeneration or anything, but it's very well made, has spike and surge protection, is UL listed and does have some minor noise cleaning. It's rated to a full, unrestricted 20amp output. When I had it, and the dedicated line, put in it was truly like an overall system upgrade. To me, like replacing all wires with better ICs and speaker cables. I heard stuff I had never heard before whether it was my digital end or analogue. It all sounded much more detailed and open with no attendant brightness and dead silent backgrounds.
OK- so that's all good, right, and I never have to think about what's happening with the rest of the house electrically again! Wrong! 
About two months ago I started hearing this very noticeable HUM coming form my Krell KAV400i integrated amp at random times of the day or night. I mean noticeable from my listening chair 8 feet away- not just with ear up to the amp! Now I know the KAV has this huge toroidal transformer so obviously something was getting into the electrical system, and that thing was doing it's job to fix it I guess, but it was annoying and worrying at the same time. Plus I was like, WTF? I thought it was isolated? What could be getting IN to a line not a part of the rest of the house?
So I had my electrician back for another unrelated job and he points out that, although my circuit is isolated in the sense that nothing other than my audio system is using it's juice, the GROUND still is connected to the same central ground as everything in the house! What?! Doh! And further more, he says short of putting two more 8 foot copper ground bars buried in my yard just for said audio system, there is no way to truly take the circuit out of the loop. And by the way, everything in the house including pipes, vents and whatever else is ALL attached to this grounding system!
Hmmmm. That sucks...and it makes me question just how much you can isolate power, no matter how expensive your re generator is, 'cause it's still going to be grounded to that whole complicated mess. And I definitely don't want to think about what it'd be like if you lived in an apartment or dorm!
So now I'm trying to rack my brain as to what suddenly changed- of course I think it has to be our heating unit. Two months ago is when we started using it a lot, and the hum was not constant so maybe it was something to do with that. It wasn't--- and the only way I was able to start to pin it down was have the electrician turn off each breaker in the house, one at a time with me on the phone at my amp, until the amp went silent again. So, in the end it was two steam humidifiers upstairs that were the culprits. They were worst when set to LOW, which I take to mean the resistance between HIGH and LOW sends out a bunch of spurious noise into the electrical system. Simple, but difficult to find and not exactly obvious. Since then a tech at Krell said to me it's not the first time he's heard of humifiers casuing problems with their amps humming.
Luckily, it wasn't something more complicated or necessary to the household, and now when I want to really sit down for some listening it's a simple thing to make sure they are both off... Anyway- the process by which I was able to solve this was very instructive to me and hopefully might help someone else here as well. Happy listening. 
OK- this is a little related to AlexO's post about the Hydra 8, but mostly just about how weird electricity can be, and how difficult it is to ever completely isolate your audio system from the rest of your house. This a longish post but I think will be instructive if you stay with me.
So here's my setup, which I wrote about before. I have a dedicated outlet that incorporates the PS Audio Soloist In-Wall Power Conditioner. My amp goes right into this outlet via an upgraded power cord (Harmonic Technology Pro AC-11). I don't think the Solist does a whole lot in the way of actually regeneration or anything, but it's very well made, has spike and surge protection, is UL listed and does have some minor noise cleaning. It's rated to a full, unrestricted 20amp output. When I had it, and the dedicated line, put in it was truly like an overall system upgrade. To me, like replacing all wires with better ICs and speaker cables. I heard stuff I had never heard before whether it was my digital end or analogue. It all sounded much more detailed and open with no attendant brightness and dead silent backgrounds.
OK- so that's all good, right, and I never have to think about what's happening with the rest of the house electrically again! Wrong!
About two months ago I started hearing this very noticeable HUM coming form my Krell KAV400i integrated amp at random times of the day or night. I mean noticeable from my listening chair 8 feet away- not just with ear up to the amp! Now I know the KAV has this huge toroidal transformer so obviously something was getting into the electrical system, and that thing was doing it's job to fix it I guess, but it was annoying and worrying at the same time. Plus I was like, WTF? I thought it was isolated? What could be getting IN to a line not a part of the rest of the house?
So I had my electrician back for another unrelated job and he points out that, although my circuit is isolated in the sense that nothing other than my audio system is using it's juice, the GROUND still is connected to the same central ground as everything in the house! What?! Doh! And further more, he says short of putting two more 8 foot copper ground bars buried in my yard just for said audio system, there is no way to truly take the circuit out of the loop. And by the way, everything in the house including pipes, vents and whatever else is ALL attached to this grounding system!
Hmmmm. That sucks...and it makes me question just how much you can isolate power, no matter how expensive your re generator is, 'cause it's still going to be grounded to that whole complicated mess. And I definitely don't want to think about what it'd be like if you lived in an apartment or dorm!
So now I'm trying to rack my brain as to what suddenly changed- of course I think it has to be our heating unit. Two months ago is when we started using it a lot, and the hum was not constant so maybe it was something to do with that. It wasn't--- and the only way I was able to start to pin it down was have the electrician turn off each breaker in the house, one at a time with me on the phone at my amp, until the amp went silent again. So, in the end it was two steam humidifiers upstairs that were the culprits. They were worst when set to LOW, which I take to mean the resistance between HIGH and LOW sends out a bunch of spurious noise into the electrical system. Simple, but difficult to find and not exactly obvious. Since then a tech at Krell said to me it's not the first time he's heard of humifiers casuing problems with their amps humming.
Luckily, it wasn't something more complicated or necessary to the household, and now when I want to really sit down for some listening it's a simple thing to make sure they are both off... Anyway- the process by which I was able to solve this was very instructive to me and hopefully might help someone else here as well. Happy listening.