[sdiy] Fixing humming transformers in 1u rack units

[MTG]

I had one situation where putting a small rubber bump-on (foot) on the 
transformer (or interior case lid ... can't remember) provided just enough 
damping to fix it.  Actually I seem to recall it was more of a buzz than a 
hum.  Also I saw a case were a shield that was interior to a unit 
(cantilevered over the transformer) was vibrating. Similar fix I think. In 
both cases these were sounds you'd hear outside the unit, not it the audio.

GB
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