Sooner or later turning on my Crown amp could kill me with the adapter plugged in?
The point is that using that cheater plug, it is NOT an adapter, is just bad and unsafe engineering.
The issue you have having is stemming from having multiple grounds with one or more at a different potential. When this occurs you have have current circulating in the grounding system of your installation. This is what creates the hum and why it is called a ground loop.
You have posted limited to no information about your system so I can't solve you problem until you map out every connection.
I should point out that cable and Ethernet connections present frequent and difficult problems due to installers not following code and not grounding their systems to your panel at entry as required by code.
Now the principle of avoiding ground loops is to have one ground in the system to which everything is bonded.
Every system needs a reliable ground back to the panel.
Now you stated that your amps are in wood. I should state that professional metal racks are worth the money, as equipment grounds can be bonded securely to metal racks. I did not do this in my previous house and that caused me a lot of extra work constructing a reliable ground plane. In the two pictures below, you can see extensive ground plane I had to build with copper to get everything quiet. I have to stress that heavy gauge is the order of the day, as there can be no significant resistance between grounding points.
In this house, I designed the ground plane for the house. In the AV room chase one of the two main panels is located.
I have three 19" pro metal racks. These are all bonded with massive braided copper cables. The racks are bonded back to the panel with stout copper braid.
I was present when the Comcast techs came to install the cable TV and Internet. The tech that came had only just started, so that encounter turned into a professorial teaching session.
The bottom line is that following code and using sound engineering procedures works. Just winging it like you have, does not.
The owner of a long time Twin Cities B & M audio stores was here a couple of weeks ago. After listening and also demonstrating the museum end of the studio, he asked: -"How did you get everything so quiet?" He noted that no matter what I demonstrated there was zero hum or buzz. I explained that it was the result of planning and sound engineering practice.
Lastly no one on these forums who wants to stay in good standing is going to countenance you not following code or engaging in unsound and potentially dangerous practice. So no matter what it takes, you need to take the high road and do it right. It will take time, effort and thought. Do not look for slap dash short cuts.
