You should use 2 things :
- the events "on start of layout"/"on end of layout"
- tags for your sounds.
At the start of layout, start playing soundtrack with tag "soundtrack".
At end of layout, stop playing "soundtrack"
(those are actions of the Sound object)
If you add a global variable in each layout, variable containing the name of the soundtrack, you can just have those 2 sound events in every layout , just using the variable to play the wanted soundtrack.