We are getting an intermittent grinding noise coming from (what sounds like) the left front under braking. I just removed all 4 wheels, and everything seems fine...plenty of pad left on the fronts (new OEM rotors/PBR metalmaster pads) and rears. The rears occasionally squeal, but it's a very different sound than this. The calipers are tight, as is all the suspension stuff. Any suggestions? This is the 2nd time I've checked it and found nothing obviously wrong, yet the noise persists.