Hegel hum?

Is the hum mechanical? 

If so it can be related to DC in your AC.  Try turning off every other breaker in the home to try to locate it. 

If you put your ear a foot from the speakers it is common to hear a faint hiss. But not a hum. This could be a faint ground loop. This would be that the amp is on a different circuit from the rest or one piece of equipment and there is a slight potential. 

To test. Plug everything into a single circuit and see if it remains. 

I should have also mentioned in my first post that the hum is not coming from the speakers. In fact, when I turn the volume up and pause the music, I hear nothing out of the speakers. It's the h400 that has a slight, even tiny hum. When I look behind the amplifier I have a spaghetti plate of wires between speakers, electric plugs, a streamer and a subwoofer but the hums not loud enough to make me try sort that mess out.

The hum is most likely coming from the transformer inside the amp. I use to hear it in my H390. Got a DC blocker and the hum went away. Since grounding the outlet the amp was plugged into I don’t hear any hum. I think what you are hearing is normal. I just purchased a Electrocompaniet intergrated and if I get very close to it, I can faintly her a buzz coming from it. No worry.

My Hegel H590 has a normal, cyclical, mechanical, ever so slight hum.  In over 25 years in high end audio, I've never owned an amp, whether it be tube or SS, that didn't have some kind of a hum.  Some hums extremely slight, and some more noticeable.  With my Hegel H590, the barely noticeable humming sound cycles out after a few minutes.