Rim seems to be shedding metal chunks
If you've used the brake pads up to the point where the metal is exposed, you've used them way too long and possibly caused some rim damage. There are wear indicator grooves on brake pads -- when they're gone, put on new pads. 

As for having metal embedded in the brake pads, I defer to this question. You might want to try switching pads (Promax stuff is generally low quality -- try Kool Stop), and checking the wear indicators on the rims.