CPU whine through one monitor speaker

[Tony Hardie-Bick]

> Bad filtering of mains power perhaps? A degraded cap in the speaker’s PSU?

if sudden, it's a dry joint

if gradual, it may be the small (probably SMD) capacitor that determines
the switching rate of the power supply, or dirt on the board that gives
the same effect

it's also possible that the mains filtering is faulty, as you say, and
what you're hearing is the normal evolution of the supply's switching
frequency, exposed by the lack of filtering

or... the circuit is getting a bit old, component values have drifted,
and the switching frequency is compensating for this, revealing a
manufacturing fault in the mains filter that was there when new

for extra points, consider all this stuff in a rocket motor system :)

t.