Depending on how old and how many kilometres the car has, it is highly likely that the front brake disks have developed a "ridge".
This ridge now actually prevents the brake pads from wearing down to the wear-limit, resulting in metal on metal from the disk ridge and the metal backing plate of the pads.
this is dangerous in that there could be catastrophic failure of the brake disk
but
it could also be as simple as the brake "anti-vibration" clip that has come off and now the brakes rattle/scrape sound especially at slow speeds
I have experienced both scenario's on my car, applying brakes at almost walking speed I heard metal on metal grinding sounds, but no warning light.
took the wheels off and inspected and discovered that the outer edge of the backing plate of the pads was actually running on the ridge of the disk.
Skimmed the disks, replaced the pads.....almost perfect
when I drove away I heard strange clattering/cluncking sounds, when braking especially at slow speeds, so turned back to my shop, off with the wheels, only to discover that my staff had forgotten to replace the "anti-vibration" clip.....a little "uit-kak" later and all was good.
if you are in Gauteng, possibly East Rand, bring it into my shop and let us look at it.
your options, dependant on the findings
1)Skim the disks...R300 per set
2)replace the entire disk
3)replace brake pads
4)possibly source a new "anti-vibration" clip