I've been using ST3 for a while now and absolutely love it. I have fully transitioned over from OnSong.
Several days ago I wiped out my hard drive and reinstalled the OS on my iMac. Everything is working fine including ST3 until today. I no longer have audio output from ST3. All other applications work well. My iPad and iPhone both have audio out for ST3, just not on my iMac.
Under settings > Audio, the Volume slider is at full left (no audio). If I move it to the right with the mouse and let go, the volume snaps back to full left.
I deleted and reinstalled ST3. Still no volume. I restarted my iMac and still no audio out of ST3.
Is there a setting somewhere I missed?
Thanks for any help.

No idea what I did, but it's working now. Sorry. Can't explain this issue and the volume under audio is still full left.
I'm just glad it works now.

Are you using the headphone socket as audio output?