Epson Scanner Machine Gun

For the first time in four months, I plugged in my Epson Professional 1660 scanner into my G4 wind tunnel, flipped on the power bar and was hit by a VERY LOUD chucka chucka chucka chucka, at about the speed of a First World War fighter aircraft machine gun and sounding much the same.

It makes the noise for 20 to 30 seconds, then a red light glows and the noise stops. But the light sometimes turns green, and the bullets fly for another 20 to 30 seconds, at which time the light turns red again and it runs out of ammo.

When I disconnect the USB cable (I tried three of them), the noise stops immediately.

I know I'm using the correct DC brick because it says Epson on it.

Anyone have a clue?