Brake noise at startup when cold
 

My truck is in Germany so it's being pounded by cold; previously in the southeast. When it gets very cold and snows, I hear a grinding noise when using the brakes on startup. It only lasts a few minutes. I don't think it's anything to worry about but when doing searches I saw that it could be the caliper? Just want to confirm if this is true and should I look at replacing. I've looked at the disks when doing a rotation no more than 2 months ago and they look smooth.