[eaglegtx]

I get the same thing. It's often damp in my area.
Sometimes, in the morning, when I leave my house for work....the brakes are as touchy as hell. It goes away within a few minutes.
As for the grinding/rubbing. I assume you hear this rubbing/grinding during very slow breaking? I'm almost positive that you don't hear it during hard to regular breaking.
Anyway. I had the same problem. It was annoying as hell, because I knew that there were new pads on the car. Here is what was causing this slight rubbing noise. Try to bear with me....it's a bit hard to explain.

My pads were on inside out.....If you know what I mean.
I'll try to explain. On your outer pad, there is a very small bump... almost in the center of the pad. If that pad happens to get installed on the inside...that bump will wear into your caliber's piston, causing a slight rubbing noise at low breaking speeds....and will cause serious damage to the piston if left un-attended.
I'm sure I just confused the hell out of everybody, so if ya wanna see some pictures...let me know. I'll show ya what I mean.