a different kind of ticking under the hood

[HeWhoKillz]

I was gonna post this with the other ticking noise but this one is different. When i set the car to the on position but don't start it and the rear defogger is on, I hear a clicking that only goes on for about 5 seconds and then quits. Without the defogger I don't hear it. I have never heard this noise before, in fact, its become a habit for me to leave the rear defogger switch on all the time and I never think anything of it and now I'm hearing it. Its a 91 corolla. Is the switch just trying to kick in or something?