Hourglass countdown

Is there any way of causing an ominous sound to be played when the animated countdown hourglas reaces zero?

Is this an API script?  If so, yes. 

I believe it is :) Is there any chance that you might point me in the right direction of how?

You'd need to edit the script to play a jukebox track when it gets to the end. Details here: https://help.roll20.net/hc/en-us/articles/360037772833-API-Function-Documentation#API:FunctionDocumentation-playJukeboxPlaylist

I haven't messed with the jukebox functions in a while, so I can't give you much more help directly. You could also look at some of the other scripts in the repo.