if the sound occurs during the first few stops in the morning, afaik its normal and no service action is required. the brakes are simply cold. you may want to clean the brakes anyway kung di ka mapakali. me uses warm water with lotsa joy dishwashing liquid kung walang brake cleaner. buhusan mo disc habang iniikot ito. 3M, wurth sabesto, prestone are among the top brands of brake cleaner that i prefer. mas mura nga lang kasi yung sabesto iirc.
madali talaga kalawangin ang brake discs due to the material used which is cast iron. kaya preferable na idrive regularly ang sasakyan para mawala kalawang. kapag kinalawang ng todo ang disc hindi na pantay ang braking action.