Rear Brakes Resonating from high speed braking

I fitted some godspeed grooved disks and some kevlar pads to my 2007 WRX. I also fitted Godspeed own front Brembo kit (PFC Z-rated pads highly recommend) which is a huge improvement over stock which frankly are just plain dangerous imo. I also had the rear calipers refurbished with new stainless steel pistons. After fitting the grooved disks the rear brakes made a slight hum from high speed which I put down to the grooves. They must generate some noise surely. Over time this hum became louder and louder to a point the whole rear of the car resonated badly. The noise also started to became noticeable from lower speed braking. The car always remained stable and the stopping performance did not seem affected. Eventually I took the rear wheels off and first checked the disks for run-out to see if they had warped. The run-out was tiny and well within Subaru's 0.0027inch tolerance. I then took the pads out and found the unworn top edge of the pad was over hanging outer edge of the disk and assumed this was dragging making the resonating noise. It also makes sense as the lip became deeper with pad wear the noise became worse. I cleaned the edges with a file and put the pads back in. The really loud resonating (buzzing) noise has now gone but I still get a slight humming noise from high speed which I am still putting down to the grooves and possibly the pad combination. Back to the same sound that they made when I first fitted them brand new. Quick and easy to check if your suffering a similar issue. I expect the noise to come back as they wear again at which point i will try a different make of pad. I am hoping that I can find some chamfered from the factory. Anyway I thought I would share in case it helps someone.