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.
Hegel hum?
Spent a week or two enjoying my new H400 and noticed a faint hum between the time I turn it on and before I play music. Also there when I pause after playing a while. Note that the hum is only apparent when I bring my ear a foot away from the amp. I’m quite pleased otherwise but am wondering if this is normal?