Nvidia card audio whine - hardware question

Hi. I am using a Linux box I picked up from a gamer who was upgrading. It has the Nvidia GTX 1070 and Z170M-PLUS Intel® Core™ i5-6500 CPU @ 3.20GHz × 4.

Recently it started making a chunking/whining sound when training. But even more recently, I discovered that the sound is actually coming via the audio cable through the monitor speakers! Not directly from the card at all. The sound is independent of the Ubuntu volume level setting.

Is there any fix, short of unplugging the audio cable?

BTW, I am a hardware ignoramus.