I had the same issue with my 2007. I tried greasing everything attached to the pedal. Seamed to help a bit, but came back short while later. Then I changed out the brake fluid. Not a sound from it since.

 

I'm having the same issue right now, i've installed stainless steel brake lines from J&M, my mechanic said they send just enough line to do the job but that the oem ones were longer.

So i'm thinking that might be the issue with my car. I'm taking the same advice and trying the grease.

 

It happened to me last year in the middle of the summer, when I was in az and super dry out. Went away slowly and never came back. But exactly what nuke said should do it!!

 

To update, 5 years later the brake fluid change apparently fixed the problem. The creaking has never returned.