I'm no scientist but I understand the difference between theoretical
noise and actual verifiable noise and that, empirically, only the
actual noise can actually be heard. by us humans. Noise needs to be
heard to exist.
Class D amps are nearly immune to any noise they (or their SMPS) might make. The switching occurs at the output of the amp to which speaker cables are attached, which might make a suitable antenna.
Its the other gear in the system that is really the concern (not to mention pacemakers and the like in the area)- they might pick up the radiated RF noise and might react poorly to it.
However, neither of these are really issues with any competently designed amp or power supply, and while I get the concern, its mostly a red herring. You would never be able to ship an amplifier (or power supply) out of the country if it made any appreciable noise!
So I don't think this is anything to be worried about.