I was about to reply that I too have heard this noise and to my shock there were a lot of replies. I left my car parked for a week and when I came back, I was pulling it out of the garage and heard the same noise. To me, it sounded like metal expanding. I assumed it was the cold garage + heat outside + engine and brakes not used for a week = sound.
I inspected the car and everything seemed normal and good to go.