In [this clutch / flywheel replacement guide](https://www.thecarpassionchannel.com/clutch-install), during the test drive, the driver says "I just chirped second gear! This car has never chirped second gear.".

I do hear the quick "chirp" sound as he shifts (into? out of?) second gear, but I don't understand what causes it or why the driver is excited about it. What's going on here?