see the Manual about preloading audio /
Only two or three sounds should be preloaded at once
and it also says:
You can also use the Preload action to start downloading an audio file without actually playing it. This can be done on Start of layout to start downloading a few important sound effects so there is no delay when they are played for the first time. However it is entirely optional (all games will work without any preloading at all), and it should not be over-used since preloading too many sound effects on startup can slow down browsers with too much downloading and result in no sound effects playing at all for a while.