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:
Select Add 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.