it's possible you're hearing the A/C compressor running. It's a 360V electric compressor so it's not dependent on the engine running. It's located low down passenger side front when you open the hood. If the sound you're hearing is from that area, it's almost certainly the compressor. I will run periodically for battery cooling as well as when A/C is selected (temp setting low enough) or defrost mode. With your screen on the climate page, look in the lower right hand corner and see if the snowflake is set to on when this vibration occurs. This indicates the compressor is turned on.