You heard a click, it means you are very close to being able to open the safe. You keep trying to open the safe, then you hear another click and the safe opens.

You quickly put everything valuable inside the safe in your backpack. And when you were closing your backpack you hear another click, but it's not the click of the safe, it's the click of a gun.

"You better put that things back, thief." You hear Jason's voice, which is distorted because of his helmet.