How does fluorescent lamp produce audible sound when blinking?
How does a lightning strike generate thunder?

The discharge into the gas pulses the atoms, while it also heats the gas. This all happens in a minute fraction of a second.

The single layer of glass can't do much to stop the vibrations this creates and as an effect you hear the glass vibrate along, giving the ticking the characteristic sound.

In flasher tubes inside big stroboscopes the tick is less flavoured, because the glass is thicker to relation, to keep from bursting at the high energy levels of the flashes.

If a starting pulse comes more as a wave, it can sometimes be that the tick is barely audible, because the last spark-over is of much lower energy. But in normal old-fashioned lamps the balast makes a sharp pulse creating a strong flash and as such a loud tick.