Creaky/Crunching Noise in my Brakes

Howdy folks,

My 2004 Prius has just recently developed a noise in the front undercarriage. The noise happens when I release the brakes after I am stopped; the problem is especially pronounced if the brake pedal is fully depressed. I hear a series of 3 or 4 "creaking/crunching" irregular mechanical noises whenever I release the brakes.The problem is not when I am applying the brakes while the vehicle is in motion. The problem started a few weeks ago and the incidents were rare and not as intense as they are now. I am going to have it looked at during my next service: 22,700 miles. I have 21200 miles on the car and I bought it in November 2003. I don't brake or drive like a maniac...in fact I got 54.5 mpg on my last tank

If anyone has had a similar experience or advice, I'd appreciate hearing it.