I recently switched audio hardware to use my headphones while editing and now since chaanging back to my macbook speakers I can't control the volume of any project. I can mute my speakers and the project still plays at the same level. It's really annoying as it's stuck on loud.
This sometimes happens for me when disconnecting or reconnecting an alternate audio source (thunderbolt monitor with speakers) from my MacBook Pro when using Premiere Pro ... go to your Premiere Pro preferences > Audio Hardware and under 'default output' select 'Macbook speakers'. That should fix it.
If not double check your Macbook System Preferences > Sound and under 'Output' ensure your device output is set to the Macbook speakers