As I mentioned a few times before, all transformers will harm when powered up without anything connected to the secondary. That's just physics, magnetic flux+laminated core = hum. Some are quieter than others, but most larger ones found in power amplifiers will hum loud enough to be audible in a quiet room and if you get close enough to it. In general, such natural construction related hum should not be audible from even a foot away, unless the room is really quiet (just an educated guess, as I don't have such a room).
I have some that were/are audible from a foot or two and some only with ears touching the chassis. If you can't hear it, either you have a higher noise floor in your room or you are not sensitive to the associated harmonic frequencies. Some would harmonize with other devices in the house that inject certain harmonics into the power line, resulted in much louder hum that obviously can be eliminated by simply turning off such device or use good quality power line conditioners/filters.
Some of the older Anthem amps hum quite loud, to the point I wouldn't consider them, but the recent MCA models are in fact silent from even inches away. Below were my findings in my own room(s)/houses:
The quite ones:
Adcom GFA-555 (no longer in use, lost in the basement) - very quiet, audible within a couple inches.
Denon AVR-3805, 1705, 1912, 4308 - very quiet, most would say silent I would think, audible with ear touching. Actually the 4308 was slightly louder, audible within a couple inches.
Marantz MM8003 - Same as the Denon AVRs
Marantz AV7005, 8801 - Same as the Denon AVRs. They should be quiet as the power transformers are small.
Anthem MCA 20 - Same as the Denon AVRs.
NAD C326BEE - Same as the Denon AVRs.
Outlaw M2200 - About the same as the Denon AVRs and Marantz MM8003
Now the louder ones:
Sony DA2ES - quiet, audible within a foot or so, from distant memory.
Sony DA4ES - medium loud, audible within 2-3 feet.
Parasound Halo A21 - medium loud even with the large toroidal transformer encapsulated, audible within a few inches. Sensitive to my variable speed humidifier.
Bryston 4B SST - About the same as the A21, may be a touch louder, but seemed totally immune to inference from other devices in the house.
Marantz SM-7 - A little louder than the Bryston and Parasound Halo.
I did press my ear on quite a few amps in dealers rooms and as I mentioned earlier I found the Anthem amps quite loud but that was more than 10 years ago for sure. Other than that, nothing really stood out that I could remember, but it was very difficult to compare in dealers rooms as one can easily imagine.
In my opinion/experience, Andrein brought up an excellent point that audible noise should be a factor. Whenever I shop for amps, I would definitely consider the weight and noise level (transformer hum). I do rank the Anthem MCA amps high because of their excellent power to weight ratio, and the quiet hum. Continuous power rating (I mean literally continuous, like Krell, McIntosh's) are not important to me at all as I have no time for highly compressed music contents.
