audio midi setup multi-output intermittent audio cracking

I have been using my rMBP and my display port's speakers together as a multi output device via the audio midi setup
Intermittently one side will get crackly audio but if I go back into the set up and uncheck/recheck one of them you no longer hear crackling
Is there any way to avoid the crackling that happens?
If not is there another way I can combine to output sources into one output that might not have the same issue.

thanks