Power supply hum transmitted to loudspeakers

I know the issue of hum and buzz has been discussed endlessly. Is it not almost universal that all amplifiers with power transformers have some low level power supply noise that will cause minimal leakage hum, buzz, or hiss through the loudspeaker with your ear close enough and no inputs to the amp connected?
Is this considered the noise floor of the amplifier? According to Galen Carol's website, if you can't hear it through the music and your system sounds the way you want it to, this idle noise should be ignored. Any thoughts?