I noticed that when I hit the button for my rear defrosters/defoggers I hear a click noise. It's not a quiet click either. I haven't done so, but I could probably hear it if I had my car around 5k (stock manifold, straight pipes, stock mufflers). To guess, although it is hard to describe sounds, I'd say it's like hitting 2 marbles together. Yes, that's kind of random, but it's the best I could think of.

Also, my rear defrost sucks. My girlfriend and I left together (separate cars of course) this morning after being parked together so we had the same amount of fog/condensation on our back windows. Her's defogged in about 1 minute. After 10 minutes of driving, mine had started to show signs of defogging. I still couldn't see out of it... at all.

Related issues?

As a side note, I did have to fix some (about 10 spots) of the lines on my rear defrost with the paint-on copper. The clicking was happening before I did this so that's not the cause. I'm thinking it might have made the defrosters work like crap though.

 

It's probably the relay you're hearing. Not sure why it would be so loud tho. You can usually hear them, but not THAT loud.

 

It's pretty damn loud. Maybe it's normal... but I haven't heard any other relay in my car click that loud except for one. That would be when I tried jumping my car and all I got was clicking from under the hood.