...emanating from my PC along with a "beepbeepbeep" from the overheat alarm. There was even smoke coming out of the box.
Don't panic captain Mainwairing!
Shut PC down a la "plug" method and looked inside. Of course it was "just" dust - but made for an interesting few moments...
Vacuum cleaner, narrow nosed adapter, suck out a hundredweight of dust. Let's see what we shall see...