Gents, they all hum, some are built for quietness but still hum if you are close enough to them in a quiet environment. I agree if you can hear the hum easily, say from a few inches away, then may be it is not "normal" but hum they do.
I can hear the fan of my Oppo well before I can hear any of the toroids in my 4 amps and I consider them normal.
It is a matter of how audible the hum is and at what level is it considered normal. That would depend on the design, build quality, size, mounting, enclosure, and finally each individual's sensitivities to the fundamental and harmonics of the power frequency.