No, you can't upload a separate sound file to each frame in your storyboard. 

However, if you'd like to add a sound file to your entire storyboard, you can do this in the Animatic Tool.  

To access the Animatic Tool, select Animatic on your storyboard: 
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Select Upload Sound, then Choose File: 

☝️ Note: The Sound field under each frame is intended for your voiceover notes. It's not possible to upload a sound file there.