The ’switching noise’ of any class D amplifier is a sine wave at the switching frequency. If the filter is properly designed, the sine wave is quite small and low power- it has to be so because the amplifier can’t interfere with other services, like AM broadcast (1.5MHz is at the top of the AM band). But an amp that is switching at 600KHz will have the same amount of noise and 600KHz is in the AM broadcast band too- the same rules apply.
An amplifier is an unintentional radiator. FCC (and others) will only test conducted emissions at <=30MHz. Radiated emissions is tested at >=30MHz.
The noise would be a square(ish) wave as the transistors are hard switching. It would become a sine due to the output filter.
Our amp (and I assume for most class D amps this is true) can be operated at full power all day long and you can hold it in your hand- they get warm but not hot. We don’t know where this will lead, but we have a goal and now we’re seeing if it can be achieved.
This is very much not the case. Most are based on modules, and those modules are not designed with thermal paths / heat sinks that will allow full power continuously or more specifically high current continuously. That's fine since music doesn't work that way. The devices normally used are not the absolute lowest RDSon, but more so tuned for good switching performance. When they heat up a lot of course, that RDSon goes up.