"Scott Dorsey" wrote in message

In article
. com,
wrote:
oh, i had an ultrasonic bug repeller. didn't work.

A lot of switching power supplies (and the cheap ones in
PCs are the worst) put out a huge amount of trash in the
50-100 KHz range acoustically. Since nobody can hear it,
manufacturers don't much worry about it. --scott

Ditto for LCD displays.