Drove to the mall fine without any issues. Parked for 1 hour. Drove off but when I applied brakes lightly the front driver side brakes would sound like metal touching metal when I gently touch on the brakes and at full stop it'll sound like GRRR....anyways I parked on the side street to take a look, nothing suspicious...drove off, issue stopped. It has been over two days and issue hasn't persisted *knock on wood*. What would cause that to happen? Seems like an one off case, can't replicate.

2013 Mustang GT with Brembo Package.

 

Sounds like a rock or other road debris got picked up between the pad and rotor. I had it happen on the passenger rear, and it was mysterious until I took the wheel and caliper off and found the little rock. Stupid thing wore a groove in the rotor so I had to replace the rotor and pads. Good luck!!!

 

Yeah, that was my conclusion as well. Though it didn't leave any groove.

 

Could also have been flash rust.