Disk brake pads are always in contact with the rotor and you will hear a muffled rubbing. That is normal.
There should be no metallic grinding or loud noises. It sounds like your noise is more than likely normal.
You might try hosing them out, as sometimes they'll pick up some grit and get a little louder.
Just be careful because they won't work well on the first couple of stops until they dry out.
