Well first there’s at least 3 different kinds of hum. First is ground loop hum which is what I covered. And yes if that’s what you have then that is the way its eliminated, by plugging everything into the same outlet. It won’t just go down. It will go away.
Then there’s DC offset hum, which is a transformer physically vibrating. This one the speakers are silent, its the transformer itself. Because of the way transformers and electricity works its also a kind of electro magnet which is why they always make that very faint hum, which is normal. Unless you have DC offset on your line, then its like the electro magnet transformer is imbalanced and so instead of a faint hum from vibrating only a little its vibrating a lot. There’s cheap power strips that will eliminate DC offset hum. Which you don’t have.
But you might have interference hum, which can happen any time a wire goes near another signal or usually power carrying wire. If you run your cable anywhere near a power line the AC in the line induces a current in it and there’s your hum. Shielding actually helps with this one, unlike the other two. And unlike the other two it would go down in level but never completely go away. Which is what you have now.
Usually the odds-on favorite when using multiple outlets is ground loop hum. But there’s nothing in the rules says you can’t be lucky enough to have the other one- or both!
Grounding the Lumin may or may not help. That's the thing about ground. What I said will definitely work. One ground always works. Every situation. Every time. But sometimes other things work, sometimes even what's wrong works. (Like one amp is fine, next one hums, nothing else changed) The rules never change just the winners and losers, yet we keep playing the game.
