Harry Bloomfield wrote:

DerbyBorn used his keyboard to write :

I used to have a separate doorbell transformer. During some kitchen work
the electrician fitted a new transformer inside the consumer unit. I can
now hear a (50Hz)buzz in the bedroom above.

I have a Friedland DIN mounted one in my CU, and it doesn't make a noise
(I tend to notice stray buzzes/hums/whines more than most people).

Most everyone moved over to modern wireless versions long ago

Which is why you wait outside those people's front-door like a muppet,
never sure if they simply haven't heard you, or if the AAA battery in
the wireless transmitter is flat ... again.