When I start my blazer for work I back up shift it to drive when I get to the stop sign I brake and make noise sounds like something cracked on the disk, calliper idk but when I break again it doesn't make that nosie anymore .. It does it only once when I don't drive my truck for a long time like 5 hours or more ... Idk what's the issue

 

take off the tire and take a look.. or head into a shop... could be a rock, or caliper... we all can do all the guessing, but until u take off the tire and take a look see... wont really know.

 

It could be rusty rotors... Once you use the brakes the rust rubs off and doesnt make that sound again... Happens to my big rig every monday morning...