I do not possess a Sorento, nor do I have any current issues with my Soul EV; however, on a previous vehicle (not a KIA), adjusting the volume during announcements permanently altered the volume level. Additionally, there may be a speed-based sound compensation feature; in my Soul, it is located in the "Sounds" or "Audio" menu. I cannot recall the exact designation, but it is not among the media player volume options, rather it is found under "System".
It cannot be adjusted; it is only either on or off, and seems to have little impact on the Soul EV.
Does it reduce the audio volume while navigation, and if not, did it previously do so? If the navigation system is malfunctioning, temporarily unplugging the 12v battery may reset it.
Merely some rambling thoughts before to retiring for the night.