What causes the sudden spool-up sound from an F-16 when enabling afterburner?
I've included a video to make it clear what sound I'm referring to:
at 1:16, I assume the pilot engages afterburner (again), and there is a sudden spool-up sound associated with this.
Am I even correct in assuming this is what's happening? I don't understand what this sound is though, it doesn't seem to appear consistently. Throughout the video, it appears the pilot engages afterburner and turns it off multiple times, but the sound only appears once.
Bonus question: What is the purpose of running the engine like this, and how is the F-16 attached to the ground?