In my experience, the simple switchers are pretty noisy.
They are designed to be easy.

dVdT control is a big thing, a switch that turns on very fast can have
oscillations due to inductance in it's emitter/source lead. Turning off
quickly causes overshoot and ringing on that side, and just fundamentally
speaking, a fast edge has lots of harmonics.   Slowing down the turn on and
turn off costs heat in the switch, and efficiency, but it lowers the amount
of harmonics generated, and lowers/eliminates any oscillation or ringing.

I disagree with the need for multilayer boards, I rarely use them.  I am
very careful about pcb layout, always returning current to it's source.   A
sloppily routed multilayer board is always quieter than a sloppily routed
two layer board, and I suppose the extra layers are always helpful, but when
I'm achieving noise levels that cause the part 15 test engineer to ask me if
I'm sure that the device is on, I think that adding extra shielding is just
adding extra cost.
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