Audio overlap --- Storyline 3

I have Articulate Storyline 3 and have built a tutorial with base slides and layers.  There is a subject intro narration for the base slide, and then there are layers for each object on the base layer.  Each object has a trigger so when you click on the object you, you are taken to the designated layer that provides more information about the object.  Trouble is, if the viewer clicks on an object before the base layer narration is completed, they are taken to the new layer which starts playing its own narration and now you have two overlapping narrations until the base layer narration completes.  How to I prevent this overlapping narration when the viewer chooses to go to a new layer before the base layer narration finishes?