Macbook Pro w/ retina display connected to Dell U3011 monitor via HDMI - periodic error message about audio
Go to the Utilities folder in the Applications folder and open the Audio MIDI Setup application. Select the HDMI Audio Device connected to the Dell U3011 monitor. Configure the audio format to "44100.0 Hz" and "2ch - 16bit Integer". As far as my minimal testing shows, this should fix the issue.