There is - they have to implement a load limit (20W or 25W IIRC), and this is normally done by using a self-resetting thermal trip. But when loaded below that, they run forever, and only get slightly warm. Lots of people leave chargers permanently plugged in them without any problem.
I flooded ours with superglue. That shut it up.
even rock solid stuff hums a bit, because the iron itself changes dimension slightly.
For a tiny transformer in a shaver socket, that effect should be rather small. It may be the plates in a poor quality transformer vibrating or the sound may get amplified by the housing vibrating. I expect that a good dose of superglue would put paid to that, whichever it is.
Of course, a large transformer is bound to hum, but it can't be beyond the wit of man to build a shaver socket that's near silent.
They're not actually that tiny. You'll find much smaller ones in many electronic devices. They wouldn't, for example, fit in a average wall wart.
If they are used as intended, for an electric razor, why would a bit of hum be noticeable?
But in general, toroidal transformers are as near silent as any. But cost more.
Weren't old transformer cores covered in shellac for the same reason? Or am I thinking of the windings?
Yes. But didn't stop them making noise for ever.
Keep an eye on those old Top of the Pops. Where the Johnny Pearson orchestra provided the backing. The bass amp on that had a G clamp on the mains transformer to stop it buzzing. The muso loved the sound of his amp and didn't want it touched.
Mount the transformer on rubber so it doesn't use the box as a sounding board.
NT
I remember car "engine mounts".
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