The brakes in my Maxima have been squeaking for a little while whenever I press the pedal. It only happens when going forward, and not in reverse. The car could be parked and when I go into drive and let off the brake pedal, I hear the noise. Here is a link to the noise. It is my rear passenger brake. Brake noise recording
That sounds to me like a brake pad moving around on the caliper. This typically happens when with excessive or uneven wear, or damaged components. Hard to know for sure just from a recording. The caliper or pads could be rusted and stuck in place.
My advice to you is to inspect the brakes. Don't take any chances when it comes to the ability of your vehicle to stop. If there are any signs of uneven or excessive wear, do a complete brake job.