You are correct; brake noises are like yours are not related to something that has always been present (weather), or something that is not typically defect related (the car is over 4 years old now..).
Instead, your noise is caused by one or more of the following:
1) brake pads are glazed, damaged, cracked
2) brake rotors have hot spots, are glazed, have a lip on the edge from brake pad replacement with a lack of machining the rotors.
3) brake pads are not secure in the caliper. Movement of the pads without insufficient shims and clips can certainly resonate noise.
Get another opinion about your brakes, and you will definitely come to a course of action to resolve your noise. Good luck.