I have a Dell S2419HGF monitor and it keeps giving me this message "Unsupported audio format set the audio output to pulse code modulation PCM" This only happens while gaming. I am using an HDMI cord.
If you're not using the monitor to plug your speakers and/or your headsets to it, then set the default audio device to your soundcard. You can do so within Sound Manager, right clicking on the sound card and setting that as default.
Mind sharing the make and model of your GPU, the drivers you're using and the version for your OS(if Windows 10)?