Hello tbarger,
Welcome to Apple Support Communities.
From reading your post, it appears your MacBook Pro speakers are very quiet and after restarting the MacBook Pro they will working normally, correct? We're here to help you take a look in to that!
Great working on troubleshooting. Next let's attempt PRAM on the MacBook Pro:
Reset NVRAM or PRAM on your Mac
If the issue persist, to isolate the issue is hardware or software. Create a new user account and test speakers. In the event the speakers are working properly, backup to time machine and reinstall the macOS:
How to test an issue in another user account on your Mac
How to reinstall macOS from macOS Recovery
If the speakers are continuing with the same issue in the test user account, we would encourage you to Contact Apple Support for further assistance.
Hopefully this helps!