Focusing away from Premiere causes playback crash
1st, make sure you don't have any equipment or 3rd party programs that interfere with the audio on your computer because, more often than not, it is a problem with that instead of the audio on the computer itself. 

I actually asked a similar question (which is specific to your question) about a third party program messing with Ableton (same as with Premiere).

I also answered a similar question (that got accepted) that covers a lot of things about different audio drivers and sound and the tendencies of both.

Since you have Hear installed, make sure to remove the leftover plugin located in Macintosh HD/Library/Audio/Plug-Ins even if you followed the correct steps to uninstall the app.