I have two issues with the participant knocking sound:
When my pc has different loudspeakers enabled to what I have selected in jitsi, then the knocking sound gets played by this device. E.g. with headset on or tuned down speakers on the pc, it is very easy to miss the knocking sound alltogether.
More prominent knocking for first participant
Imho the first participant needs an a) more prominent knocking sound and b) a recurring knocking sound. Because many times a moderator before the actual beginning of an conference may not be in the room (“I need coffee!”) or otherwise working on the computer with another window overlapping the jitsi screen, so that the visual notification can not be seen. This is not needed after the first participant has been accepted and the conference has started.