Need newbie explanation on grounding components.

I had some hum once. I tracked it down to a pesky pre-amp. When I replaced the pre-amp the hum went away. You can imagine how ticked I was after adding three dedicated circuits with dedicated neutrals and an isolated ground.

Being an electrician by trade the circuits only ran me about $100.00 in material and half a day in labor.

My point being the cleanest power in the world won't always help your hum problem.

Hi Darryl,
Before you do anything, call your power company and have them come out and check the ground to your service. They will (should) do this for free and most times the power company will check the outlets as well as a customer service. If that checks out ok, proceed to what Phild said. And what he said about the adapter plugs that eliminate the ground pin is absolutely correct. You need only one component grounded at the outlet, all others ground through interconnects that are properly designed. These adapters are very inexpensive. Probably less than the shipping on a "tweak", and a lot more effective. If after that you still have problems, power down, remove the adapters and plug back in, remove 1 pair of interconnects completely from the system and power back up. Repeat this, removing a different pair each time. Once a pair passes, they are plugged back in after power down, and the next pair removed prior to power on. It's a process of logical elimination. It could be a bad interconnect, or it could be a component, and that would not be discovered until you fail this test. It's a process of elimination, keep logically eliminating more until you find the culprit. The absolute last thing you should do is buy a tweak. This is a problem, that is a bandaid, and electronics don't heal well. Tom

As a total non techie, is this mainly an issue with older amps or kit? I say this as I have the "play around with different equipment itch" and I have had the humming issue only twice.
The first was putting in an OLD Bryston 4B amp. Eliminated by cutting off the earth prong in the plug.
My current (ha ha) issue is now with a pair of OLD Threshold Nelson Pass monoblocks. The are both  buzzing loudly but I suspect that the single ended Audioquest subwoofer cable (the amps do not have balanced inputs) that I put in temporarily may be the issue as I had nowhere to hang the little earth wire. My cable techie has suggest I put in his own built single ended cables which should eliminate the (probable earth) hum. The chances are against BOTH monoblocks being faulty somewhere. I will find out next week when I am next in situ.