Date   : Sun, 18 Oct 2009 21:04:34 +0000
From   : zeem.uk@... (Alex Taylor)
Subject: Dual drive power supply

2009/10/16 Rick Murray <rick@...>:

> There are two "hums" I can think of.

> A low pitched hum (50Hz)

My old Alba-branded alarm clock did this. When placed on the
chipboard-construction drawers next to the bed, it made a stupidly
loud hum that I ended up preventing by putting the alarm clock on a
rolled-up pair of socks. Eventually I replaced it with an Audioline
alarm clock that sets itself by the radio time signal, picked up for
free after it was dumped at the junk auction I go to.

> A really high pitched whine (not so much a hum), fairly similar to the
> sound camera flash units make when charging

I recently set up a HP PC for someone at work, a 4-year-old or so
Pentium 4 tower that was removed from the school's main office. It
appears to make a really irritating and quite loud high-pitched whine
when switched off, a noise which seems to stop when the PC's switched
on. I left it as it was because I'm not going to have to work in the
same area, and the person in that office may well not be able to hear
the noise anyway.

-- 
Alex Taylor