I didn't notice this until recently, because it's not loud enough to hear over the stereo. So I'm not 100% on how long they've been making the sound. I never heard the squeal sensors going off though. I had the stereo off the other day though and the grinding noise was very noticeable.
It doesn't seem to do it much (if at all) at higher speeds. But the closer I come to a complete stop, the worse it seems to get. Stopping distances seem to be the same as they've always been. Although I must concede it is possible that a gradual decline has numbed me from accurately measuring that. I certainly would not say I'm having any trouble stopping in time or quickly when need be however.
I bought my 04 WRX used, and the previous owner had upgraded the brakes. I believe the calipers are XTR or SXT or some similar acronym (they're red with white lettering and look bigger than stock, but I forget the exact name) and I think the rotors are aftermarket too. I asked the guy about the brakes when I bought the car, but that was 2 years ago so I don't remember exactly what he had done. Can't remember for the life of me what brand the pads are either. In any case...
What am I likely looking at here? Worn out pads and/or rotors? Loose calipers causing uneven braking?