HUM - you can catch fish in a dingy too.

You can go buy a six-figure bass boat to catch fish, but you can catch the same fish out of a $200 rowboat.

So, I had - HAD - a hum problem in my system that was driving me nuts for about a year. It started out that it was the amplifier making the speakers hum even when the source or pre-amo was disconnected. Then I got a new preamp and the amp was quiet but the hum returned as soon as I took the preamp off mute - basically the hum jumped components, which left me drooling in rage and confusion. I switched sources, switched cables, switched ICs and speaker cables, added a power supply then plugged everything directly into the wall.... Arrrggghh!!!

Finally, in desperation I did something that I don't like for a number of reasons: I stuck a 35 cent cheater plug between the pre-amp and the power supply (which is itself still grounded) and the hum FINALLY went away. $15,000 worth of audio jewelry and it took a 35 cent piece of plastic to make it work right. Sometimes we are too smart for our own good. Just thought I'd share.
Sorry you struggled for so long with this problem. A cheater plug should have been one of, (if not the first) things you tried.

I have several of these within reach to eliminate such a problem. I have used them a few times and usually they work just great.

Glad you traced down and solved your hum problem.
Good find, but you may still not be home free. Some of the experts here might wonder if you could be placing your $15K system at additional risk. You may want to check some of the old Agon threads regarding cheater plugs.
The good news: this may be a great diagnostic clue on how to solve this (grounding problem?) without the cheater plug.
One other suggestion - buy a polarity (outlet) checker and make sure the wall socket is correctly wired and grounded. If it isn't, not only could that cause the hum, but it also creates a shock hazard. The checkers are $5 or so at hardware stores.
Cheater plugs are a poorly kept secret I think. I've used them off and on for years usually on a pre-amp/amp combo keeping at least one properly grounded. I disregard the braysayers regarding risks. Interestingly yesterday I was reading a highly regarded amp designer/manufacturer's comments about how to avoid hums - use cheater on pre-amp. And he wasn't the first either.

FWIW I just went thru a hum problem. A real PITA but ultimately I found that the hum was corrected after I used a cheater on all of the sources ahead of the (integrated) amp. I think the amp may have an inherent design issue. I've never had this problem before with either a pre-amp or an integrated amp.
Just picked up your earlier thread... looks like you have all the advice you need. ...Tight lines.
See the comments I just posted in your original thread on this problem.

-- Al
"I disregard the braysayers regarding risks."
Excellent! ..that would make for an interesting epitaph.

Grimace, glad you feel safe with your solution, and who knows, it may be just fine. Besides, if you do have a problem, I'm sure that Newbee will step up and pay for half the damages.
Grimace....I hate to break the news to you, but by using a cheater plug, you are ruining your now hum-free sound. I suggest you find the grounding problem and do it right.
I have no idea if this will solve your problem, but I took a look at your system pics, and it looks like the amp is next to the TT and the preamp is under it? Perhaps reposition those components? Try the amp on a floor with some sort of platform or coupling/decoupling, once you sort out the hum issue?
Hum is one of my nightmare issues, because I run really efficient speakers and you can hear every gremlin. You might also look at what else you have plugged in, even if you are using dedicated lines. I know that a humidifier plugged into a bedroom will create hum in my system, although i have a separate subpanel and dedicated lines. Ditto, some low intensity lighting in our kitchen.
Good luck. I came from the 'Burgh. Used to go to Opus One, long gone.
Well again, the power supply - a PS Audio something-or-other - is still grounded. The cheater is between the preamp and the power supply, and the power supply still has a protection circuit, so I think the risk is pretty low. The amp, which is the big power draw, is still grounded.

I might check on the polarity thing though. It couldn't hurt.
I remember a story told to me by a California Highway Patrol Officer during my traffic ticket class. Very fun and funny class believe it or not and we were laughing from start to finish, but we learned lessons. He kept interrupting his stories with the words "I think I can make it" Whereby, all traffic offenders would constantly think this before they did something stupid or foolish. Everytime, before he would recite some traffic story or horrific accident, he would say "I think I can make it" The same holds true in the case of electricity and the very foolish desire for many to bypase their home and system electrical protection by using a $0.35 cheater plug to eliminate the house's ground protection. "I think I can make it". No problem until you have that one electrical fault that you never saw coming. Does anyone ever really expect an accident or see it coming? Your equipment will fry, you, your family, pet, kids, wife, etc. will be electrocuted if you bypass your ground protection by this simple and easy $0.35 fix. it is there for a reason. You are not an electrician. Well most of you are not. Please do not use cheater plugs. It is relatively simply to determine which component is causing the ground loop or hum. this is discussed in detail in previous posts and If you desire I can give you a step by step instructions on how to find the problem. Typically, when all is said and done, it could be a home wiring problem (which is potentially dangerous anyway and should be corrected) or some piece of your system is faulty. isolating equipment like we demonstrate will tell you which is faulty. now faulty may mean simply that the internal grounding is not well thought out and the equipment should be repaired or replaced. You have to understand that some designers are very good with analog audio circuitry but are lacking on electrical star grounding techniques, or they connect the signal ground to system or chasis ground which is also a no-no, and that very good piece of equipment will cause a ground loop because of faulty internal grounding. using a cheater plug doesn't fix anything. It masks an existing electrical problem which will eventually come back to haunt you in very nasty ways. "I think I can make it"

please find and fix the problem.

Look at any "dimmer switches" you may have in your home. Notorious source of hum.