Check the i/p fuse block. See if some relay is energizing on and off? If a relay is acting up, you may be able to put your finger on it and feel the vibration or heat. Also, check the fuse box under the hood, passenger side, that is close to firewall.
You should be able to remove glove-box liner, can you locate the noise?
December, 8, 2012 AT 8:53 PM
Could be your a/c door actuator that opes and closes depending on whether u want outside or recirculated air in car. Open hood and on pass side take cover off under wiper and remove cabin air filter. Look behind it and u might see that actuator stuck between open and close. Hope this helps.