Hegel hum?

all transformers humm, some very much so. Usually they are bolted in tightly, or have some elastomer in the bolt to quiet the humm. 

You may have an issue where the transformer has loosed up, and is being allowed to vibrate. If it has elastomer it might have been squished out, deformed, or come apart. 

Pull the amp out, disconnect from everything, pull the case, and see if you can move the transformer around. Also check to see if anything holding it down is loose. If it has elastomer, it should be "tight" but not so much so that the elastomer disformed too much, or gets pushed out. 

It's like a 10min fix, also normal.

My solution to the nest of wires (I have the Hegel H20 amp) is to seperate all interconnects and speaker wires from AC cables. I put that black foam pipe insulator with the slit in the middle  (cut into several pieces) to seperate all the low power interconnects/speaker wires from AC cables, just slip it over the interconnect and AC cable, cheap and effective.

Sounds like either a combination of cables picking up AC and/or DC gettting into your power lines, several products out there to clear up DC on power lines which make transformers hum as many have noted.

Your system is deserving of power conditioning, I like the Puritan PSM136 conditioner with groundmaster and some Verifi audio plug in thingies, astounding how much improvement that comes from cleaning up the power.

My experience with high current Class A or Class AB designs with large power transformers like Krell and Classe is that they normally produce a faint mechanical hum when first turned on as transformer charges and “warms up”.  The hum should not be audible after warmup.  I am not familiar with Hegel in general, but the H400 specs indicate it is a high current design with a large power transformer, so some hum on warm up may be expected.  You state this occurs after warm up. This does not appear to be normal.  I would contact Hegel for recommendations. 

It does not appear you are hearing the hum from your speakers.  If you are not hearing it from your speakers I would not expect it to be  ground loop hum.  If you are hearing it from your speakers, I agree with others to experiment with removing ground loop hum. See the link below that explains ground loop hum and how to attempt to remove it.  If that does not solve the problem, then contact Hegel   

https://www.sct.com.tw/articles/4-effective-approaches-that-eliminate-ground-loop-video-audio-interference

I've had preamps and amps that were sensitive to DC on the line before.  I've tried many DC blockers and pretty much all of them hurt the dynamics.  The one that I found to work best and not hurt my system dynamics is the Emotiva CMX2 AC Line Filter With DC Offset Eliminator.  It is a great design and does what it needs to do, nothing more.  I have one extra used one with the LED lights not working (a common reported problem) that I could let go for $75 plus shipping if you are interested.  My new Atoll IN200 evo integrated does not hum at all in the same house and location.

In fifty years of owning high end audio equipment I have never heard a hum coming from any of my components. 

You may try to contact Hegel and explain to their technical support staff this issue..? I would return such amp to manufacturer, if no help etc.. Foot away hum isn’t good, few inches could be okay..

I had many amps, and the only accuphase designs have zero transformer related hum noise. some transformers can be fixed by potting them in qualified epoxy, or putting transformers on shock absorbing spacers.

As the OP I offer thanks to everyone for their suggestions. I’ve never spent this much on a stereo component and was hoping for some assurance that nothing was amiss. From now on I’ll resume my listening position and enjoy the music.

Props to all who responded above. Very thoughtful and correct advice.

If you’re not hearing a hum/buzzing from the speakers your concerns should be minimal.

The Hegel integrated amps don’t turn off/on. They switch between standby (very low power consumption) to on (full power & ready to rock)

When transitioning between standby and on the system will fully saturate with current. In so doing the first thing in the chain which is that large transformer will charge up. Charging up is a physical process where the transformer’s copper wires wrapped around the core can micro-vibrate and can cause noise (hum).

This process should stop and the unit should be very quiet after warm up. If the hum persists, then as described by the proper comments above, there is some order of DC imbalance.

If you’re not hearing it from the speakers and can’t hear the physical hum from the amp at your listening position does it matter? I hope you enjoy your listening experience.

hum out of speaker indicative of ground loop 

hum out of box indicative of DC offset causing toroidal vibration

hums are annoying. You might try a DC filter ...ala,

https://avahifi.com/collections/accessories/products/humdinger-dc-line-blocker

Seems most audio systems are enjoyed having your ears equidistant from the speakers, rather that a foot from the amp 😉

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.         

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.

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.

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. 

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. 

I would think and hope no hum is normal and desired.