high-pitched noise during bootup

[Richard Smith]

> I've heard something like it too, and when I commented on it to MarkF he
> said it's normal and is part of the DC electronics stepping down the
> voltage (or something like that).  Somewhat like the high-pitched whine
> you can hear from the high-voltage flyback transformers in television
> sets and other CRT-based displays.  Maybe that's what you're hearing?
> Maybe check if it comes from the area around the power plug or not.

You are hearing "inductor whine."  In a switch mode power supply the
dynamic currents inside the inductor can be quite large.  This causes
the windings to vibrate due to the magnetic forces on each winding
sometimes causing whine.

Generally the more you load the power supply the more they whine and
its mostly harmless.

-- 
Richard A. Smith