2004 Beeps for 15 seconds
 

My 2004 V6 Mustang started making a 15 second long series of beeps when the key is set to ON. This series of beeps (about 30) has no pauses, the Airbag light does work, and does not flash indicating a problem. The sound is coming from behind the instrument panel. There is no other indication of a problem.

Any ideas?