1994 Altima - Loud Buzzing Under Dashboard

My 1994 Altima has a continual loud buzzing noise under the center dashboard everytime the ignition is turned off. It's been buzzing non-stop for the past two days. When I start the car, the noise goes away. Does anyone have a clue as to what this problem might be?

Thanks!
Doug

Check under your dash ans follow the sound, I think its the key in ignition sensor.