If in fact your brakes still have sufficient friction material (the acutal wearing braking material)left, noise on braking is most likely caused by either: poor surface finish on the brake discs themselves, such as the normal accumulation of wear or from previous damage from completely worn out pads, or as others have already suggested, the quality, or the lack thereof, of the brake pads that are currently installed.
The discs should be resurfaced on the car using one of the approved refinishing machines whenever there is out of limit runout, parallelism OR surface irregularities (grooves).
A much less common source of noise, but more dangerous, is when any of the caliper mounting bolts are not tight. Typically this would make a clunk, but since you have what you believe is abnormal noise, you should have the basics checked out.
Steve