I'm confused, are we listening for a "knocking" or a "squealing" sound?
Since you keep moving backwards after each time, rather than moving forward I'm assuming the "knocking" sound is from either braking or releasing the clutch lever suddenly, maybe even putting your foot down? It's really hard to tell based on this potato.
As for a "squealing", not hearing that at all in this.
Ultimately, if you think theres a problem take it to a mechanic, have it inspected.