This happened to mine just last week
A really fast ticking sound that's constant, loud and repeats like a stop watch ticking. It will only get worse in the next week or so if you don't get it fixed.
Last year I installed an in-cabin air filter and everything has been fine. Last week I got the loud clicking behind the glove box and took it to the dealer. They advised it was the wrong filter and removed it and I haven't had a problem since. They said it was keeping the air doors back there from opening up correctly. I haven't had one click since they removed the filter.
Now, as far as the filter I used one from that thread here that many others said they used and not the oem filter. My filter didn't have the notches cut in the side and I'm not sure if the OEM one does either. They returned the filter to me and it looked distorted from the filter door tabs pushing into it.
Now, as far as why it happened last week? This is just a guess but I was going down the freeway last week and hit a pothole really hard which made a loud thud noise when it happened. My guess is that it dislodged the filter or something and a bit of it started preventing the air doors from opening correctly. The only other thing I did was have the Fast Intentions exhaust installed last week as well. If anyone has the oem filter does it have notches in the side to accomodate the plastic tabs in the filter door?