Francisco,
In principle, I agree with you. But from a pragmatic point of view, I just don't think that is possible in each case. Let me give you an analogy from the pharmaceutical industry. I know of a drug that when given as an eye drop, will lower the intraocular pressure. This is a useful property to treat glaucoma, which is a disease of high pressure in the eye. Unfortunately, the specific drug I mentioned also causes redness of the eye, which is not a desirable property. We call this effect a "Type 1" effect, which means that the mechanism by which the drug lowers the intraocular pressure is also one that causes the redness side effect. A tremendous amount of work has been done to try and separate these properties, but they have thus far been unsuccessful. So bottom line, if you want to use that drug, you have to take the "good" with the "bad". Both are inherently intrinsic to the same mechanism of action of the drug and one cannot be separated from the other.
Now, lets apply this to the research you propose to do to try and get to the bottom of what might be causing the hum effect in a particular piece of gear. Yes, with enough time, diligence and effort, you may be able to get to a root cause that might be able to be identified, and subsequently eliminated, thus removing the hum problem. However, that may not be the case.
If, for example, my Lampi GG2 (or any piece of gear) may have, for whatever reason, some stray capacitance leak to ground that causes common mode noise and hence hum, that may not be able to be altered as it might be part and parcel of the overall design (even if inadvertently so).
post #28: https://www.whatsbestforum.com/thre...sing-rca-connections.30014/page-2#post-626565
I doubt any manufacturer intends to build in capacitance leakage to ground as part of their design but still, it might be there nevertheless. Moreover, if you ask them to check the product, they will likely respond that the product is perfect and that nothing is wrong. Sound familiar? It seems that this certainly happened to several owners who suspected their gear has a problem, only to be told it does not because it's "perfect".
So for all the good intentions that accompany identifying the root cause of hum in a particular piece if equipment, I'm skeptical that the result will be successful in all cases. (How many manufacturers are going to tell you their design has an intrinsic defect? Better yet, how many would even know how to test for one? Can you tell me of even a single one who checks capacitance leakage to ground, or common mode noise, before releasing their product? I have NEVER seen that as a published product specification for any audio product, have you?)
That is why, despite all efforts to find the culprit, the more satisfying solution might be simply to try and eliminate the hum even if a root cause cannot be found. And that brings us back to square one. Once you've tried and have take more Prozac than you think is reasonable, just try the obvious solution. Try something like a Furman isolation transformer. I repeat- it's easy to try, relatively cheap, and generally fully returnable within 30 days! What do you have to lose? If it works, great. If not, well, then it doesn't but at least you've checked off a very important box.
Marty