Brake grinding noise

[2008]

I replaced a friends brake pads yesterday. When she left everything was fine. I live about an hour and a half away, and by the time she got home she called to tell me there was a bad grinding noise coming from the brakes. I drove her car this morning, and the grinding noise is constant. It does sound like it's coming from the brake area. When you first start driving you don't hear it, even when braking, if you're going slow. Once you pick up speed, you hear this grinding/scraping noise continually and it gets louder when you brake. I haven't had a chance to look yet as we're both at work. My first thought might be the caliper piston is frozen. I wanted to get any other thoughts as to what it might be before I jack the car up, so I know what to look at. Also, if the caliper is frozen, what do you do to fix that? Anyway....please any suggestions???

Kayleen