Ramps1.4 led Lit Up and Beep---Warning?

When I was printing today, one of the LEDs on the ramps 1.4 board was lit up and I heard a kind of beep sound. When I unplugged the USB cable to my computer it stopped. It wouldn't stop whether the PSU is off or not though.

Is that a kind of warning? I'm nervous now.

Thanks.

EDIT: I think the LED that was lit up was LED3.

Edited 1 time(s). Last edit at 04/11/2014 08:09PM by jpan.

Well LED 3 is fan output generally. I would start another print and just monitor it.

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Waitaki 3D Printer

OK, The beep was actually coming from the fan...

Sorry for any confusion