On 2 Mar, 01:48, Jim Land wrote:
James Sweet wrote in news8EFh.6020$RN6.3214
@trndny07:

That's a switchmode power supply....

Switchmode power supplies do not hum. (Where "hum" is defined as a 50 or
60 Hz, or 100 or 120 Hz sound.) They operate at much higher frequencies.
Which is the whole point of a switchmode power supply: higher frequency
means less iron.

Original poster: What did you hear from this power supply that got this
whole thing started? Describe the sound.

here's a recording , putting my mic near it
it's an mp3 file about 1 minute long
http://tinyurl.com/3xsuay

around 11-15sec is probably most representative, i.e. quite high
pitched. Though it's quite a bit higher than the recording has it.