What your experiencing is the rust layer that forms very quickly between the rotor and the brake pads. It happens in various degrees depending on how damp the air is and how much moisture is left on the surfaces when you park it. The more metallic in your pads is the bigger the pop when they release. I try and drive my car around the block after washing so they are fairly dry when I pull into the garage.
It’s not harmful, provided the car isn’t sitting for months and the rust patch is scrubbed off after a couple of normal braking cycles. If you want to see it, just stop after the pop but before your wheel makes a complete turn. You will find an rust patch the shape of your brake pads on the rotor.