My Linux box beeps when I reboot it.
To the casual observer, there's nothing mysterious about that; most PCs beep when you reboot them.
The thing is, there's no speaker in the case. The speaker pins on the motherboard aren't connected to anything. There is a soundcard built into the motherboard, but I haven't connected any speakers to it. There doesn't appear to be a piezoelectric element on the motherboard.
There's nothing on or in that machine that should be able to make an audible beep.
And yet... it beeps.