Brakes Grinding

I have a 1998 Taurus V6 3.0 with 119,000 miles. I changed the front brakes almost 2 months ago myself and had no problems for about 2 weeks. The weather started to cool down to under 100 ( I live in PHX) and the brakes started making grinding sounds, but only the first time or 2 that I press the brakes. I took both front tires off and visually checked the pads and the rotors and they are the correct distance away from the rotor and there are no visible scratches on the rotors themselves. The calipers are screwed down plenty tight enough on both sides as well. The new pads are metallic and I don't know if it is just them breaking in or it is normal for metallic pads but I dont want to take any chances on ruining something. Any Ideas?